The 34th International Symposium on Lattice Field Theory (Lattice 2016)

Jul 24, 2016, 6:00 PM → Jul 30, 2016, 1:00 PM Europe/London

Highfield Campus, University of Southampton

The 34th annual “International Symposium on Lattice Field Theory” will bring together a global community of researchers from theoretical particle physics and quantum field theory, who employ theoretical, numerical and computational methods to study the properties of strongly interacting physical systems – above all Quantum Chromodynamics (QCD), the theory which describes the interactions of quarks and gluons and how they bind together to form the particles we see in experiments. The Symposium is returning to the UK for the first time since 1997, when it took place in Edinburgh, and has never before been held in England.

 

Sunday, July 24

Registration

Monday, July 25

Registration

Welcome

1 Welcome

Speaker: Prof. Sachrajda

Slides

• Coffees_and_Lunches.pdf
• ConferenceDinner.pdf
• GroupPhoto_PosterSession_Excursion.pdf
• OtherConfs_copy.pdf
• plenaryslide.pdf
• Proceedings.pdf
• Welcome.pdf

Plenary Session

Convener: Prof. Robert Edwards (JLAB)

2 From Spin Models to Lattice QCD – the Scientific Legacy of Peter Hasenfratz

From Spin Models to Lattice QCD – the Scientific Legacy of Peter Hasenfratz

Speaker: Urs Wenger (University of Bern)

Slides lattice16_wenger.pdf

3 Review on Hadron Spectroscopy

I review the recent lattice results on spectroscopy and resonances in the past years. For the conventional hadron spectrum computations, focus has been put on the isospin breaking effects, QED effects, and simulations near the physical point. I then go through several single-channel scattering studies using Luescher formalism which has matured over the past years. The topics cover light hadrons and also the charmed mesons, with the latter case intimately related to the recently discovered exotic XYZ particles. Other possible related formalisms that are available on the market are also discussed.

Speaker: Prof. Chuan Liu (Peking University)

Slides Latt16_CLiu.pdf

4 Resonances in Coupled-Channel Scattering

Excited states in hadron physics are seen as resonances in the scattering of lighter stable hadrons like $\pi$, $K$ and $\eta$. Many decay into multiple final states necessitating coupled-channel analyses. Recently it has become possible to obtain coupled-channel scattering amplitudes from lattice QCD. Using large diverse bases of operators it is possible to obtain reliable finite volume spectra at energies where multiple channels are open. Utilising the finite volume formalism proposed by L\"uscher and extended by several others, scattering amplitudes can be extracted from the finite volume spectra. Recent applications will be discussed where the energy dependence of scattering amplitudes is mapped out in several quantum numbers. These are then continued to complex energies to extract resonance poles and couplings.

Speaker: Dr David Wilson (University of Cambridge)

Slides DavidWilson_Lattice2016.pdf

11:00 AM Coffee Break

Plenary Session

Convener: Prof. Yoshinobu Kuramashi (University of Tsukuba/RIKEN AICS)

5 Hadronic contributions to the muon $g-2$ from lattice QCD

The overall accuracy of the Standard Model prediction of the anomalous magnetic moment of the muon is currently limited by hadronic effects. I review the status of lattice QCD calculations, aimed at providing precise estimates for the hadronic vacuum polarisation and hadronic light-by-light scattering contributions, respectively. In the case of the leading hadronic vacuum polarisation contribution I will focus on systematic effects in current lattice simulations and outline the progress made in computing the contributions from quark-disconnected diagrams. For the hadronic light-by-light scattering contribution the different computational and conceptual strategies employed by various groups will be reviewed.

Speaker: Prof. Hartmut Wittig (University of Mainz)

Slides Wittig_gm2.pdf

6 Towards a theory of the QCD string

I will review recent advances in describing the dynamics of the QCD string (confining flux tube) both on theoretical and on lattice sides. I will argue that combined efforts of theorists and lattice practitioners may result in a dramatic progress in our understanding of the world sheet theory of the QCD string in the nearest future.

Speaker: Sergei Dubovsky (NYU)

Slides Lattice.pdf

12:45 PM Lunch Break

Chiral Symmetry

Convener: Dr Andreas Athenodorou (University of Cyprus)

7 First Experiences with Overlap Fermions based on the Brillouin Kernel

First experiences are reported with overlap fermions which employ the Brillouin action as a kernel. After discussing the dispersion relations of both the kernel and the resulting chiral action, some of the physics features are addressed on quenched backgrounds. We find that the overlap with Brillouin kernel is much better localized than the overlap with Wilson kernel. Also a preliminary account is given of the cost of the formulation, in terms of CPU time and storage.

Speaker: Dr Stephan Durr (University of Wuppertal)

Slides durr_lat16_talk.pdf

8 QCD with Flavored Minimally Doubled Fermions

I discuss QCD with Flavored Minimally Doubled Fermions as sea quarks. Minimally Doubled Fermions are an ultra-local formulation that realizes a non-singlet chiral symmetry with only two real fermions at finite lattice cutoff, but break the hypercubic symmetry as well as some discrete space-time symmetries. I show that the broken discrete space-time symmetries do not affect vacuum since the corresponding symmetry breaking terms cancel exactly in the fermion determinant. With a non-singlet mass term, I introduce a well-controlled definition of flavor in the continuum limit which is consistent with the naturally emergent flavor structure of meson correlation functions at finite cutoff.

Speaker: Dr Johannes Heinrich Weber (Technische Universität München)

Slides lat16_weber.pdf

9 Chiral condensate from OPE of the overlap quark propagator

Using 2+1-flavor domain wall fermion configurations, we calculate the overlap quark propagator in the Landau gauge. Then we try to extract the chiral condensate from the operator product expansion of the quark propagator in momentum space.

Speaker: Zhaofeng LIU (Institute of High Energy Physics, Chinese Academy of Sciences, Beijing)

Slides lattice2016.pdf

10 Determination of chiral condensate from low-lying eigenmodes of Mobius domain-wall Dirac operator

We calculate the spectral function of the Mobius domain-wall Dirac operator utilizing a stochastic eigenvalue counting technique. From the low-end of the spectrum we extract the chiral condensate in 2+1-flavor QCD, and take the chiral and continuum limits. Lattice ensembles are those generated with Mobius domain-wall fermions at a~0.080, 0.055 and 0.044 fm.

Speaker: Dr Shoji Hashimoto (KEK)

Slides chiral_condensate.pdf

11 Staggered domain wall fermions

We construct domain wall fermion operators with a staggered kernel and investigate their spectral and chiral properties numerically in the Schwinger model. In some relevant cases we see an improvement of chirality by more than an order of magnitude compared to standard domain wall fermions.

Speaker: Dr Christian Hoelbling (Wuppertal University)

Slides talk.pdf

Hadron Spectroscopy and Interactions

Convener: Sasa Prelovsek (University of Ljubljana)

12 Heavy and light spectroscopy near the physical point, Part I: Charm and bottom baryons

We present results of the hadron spectrum using $n_f=2+1$ ensembles with pion masses as low as 156(4) MeV, we place particular emphasis on measurements of the singly and doubly heavy charm and bottom baryons. Using the Tsukuba tuning for relativistic charm and NRQCD for the bottom quarks we perform measurements of both light and heavy mesons as well as spin-1/2 and spin-3/2 baryons for all possible flavor combinations. Our subsequent analysis yields masses with an accuracy below the $1\%$-level and therefore splittings with good statistical precision. All results are extrapolated to the physical pion mass via a tightly controlled, short, chiral extrapolation.

Speaker: Dr Renwick J. Hudspith (York University)

Slides heavy-light-spectroscopy-baryon.pdf

13 Heavy and light spectroscopy near the physical point, Part II: Tetraquarks

Having introduced the ensembles and basic spectrum in Part I, we focus on results for a doubly heavy tetraquark candidate, $qq\bar Q \bar Q$. Based on phenomenological observations regarding heavy baryon systems, we motivate two possible lattice interpolating operators: a diquark-anti diquark and a meson-meson. We show these operators exhibit good behaviour both in terms of lattice QCD and their phenomenological interpretation. In particular we study the $qq\bar b \bar b$, $qq\bar c \bar b$ and $qq\bar c \bar c$ with $qq=ud,us$ flavor combinations and analyze their binding. In the chiral limit, at finite lattice spacing, we find strong indications for binding of the $qq=ud$ tetraquark candidates. We comment on possible search windows for experimental confirmation.

Speaker: Dr Anthony Francis (York University)

Slides heavy-light-spectroscopy-tetra.pdf

14 Lattice QCD searches for tetraquarks containing charm quarks

We present searches for tetraquarks in lattice QCD with quark content $cc\bar{q}\bar{q}$ and isospin-1 $c\bar{c}q\bar{q}$ which are especially of relevance to the experimentally observed charged $Z_c$ states. Utilising the variational method, we employ a large bases of operators consisting of diquark-antidiquark and meson-meson operators. We show the spectra determined across a range of channels. We discuss extending our study to the isospin-0 $c\bar{c}q\bar{q}$ sector.

Speaker: Mr Gavin Cheung (University of Cambridge)

Slides talk.pdf

15 Including heavy spin effects in a lattice QCD study of static-static-light-light tetraquarks

In previous works we predicted the existence of a $\bar{b} \bar{b} u d$ tetraquark with quantum numbers $I(J^P) = 0(1^+)$ using the static approximation for the $\bar{b}$ quarks and neglecting heavy spin effects. Since the binding energy is of the same order as expected for these heavy spin effects, it is essential to include them in the computation. Here we present a corresponding method and show evidence that binding is only slightly weakened and that the $\bar{b} \bar{b} u d$ tetraquark persists.

Speaker: Prof. Pedro Bicudo (Universidade de Lisboa)

Slides Slides.pdf

16 Lattice QCD study of heavy-heavy-light-light tetraquark candidates

We study $\bar{b} \bar{b} u d$ and $\bar{b} b u \bar{d}$ four-quark systems using lattice QCD. The heavy b quarks are treated either in the static approximation or by using NRQCD. Both for $\bar{b} \bar{b} u d$ (quantum numbers $I(J^P) = 0(1^+)$) and for $\bar{b} b u \bar{d}$ (quantum numbers of $Z_b$, $I(J^P) = 1(1^+)$) our results indicate the existence of a four-quark bound state, i.e. a tetraquark.

Speaker: Ms Antje Peters (Goethe-Universität Frankfurt am Main)

Slides lattice2016.pdf

17 Searching for evidence of diquark states using lattice QCD simulations

In recent years, exotic hadrons called X, Y, Z which cannot be explained by the quark model have been found one after another. For example, the tetraquark state, which is one of the typical scenarios to interpret the exotic state, is based on the existence of a diquark state. The discovery of a pentaquark state at CERN in July last year also makes a diquark state even more important. It is well known that an attraction between two quarks can be enhanced in the color anti-triplet, flavor anti-symmetric, spin singlet, positive parity channel and this diquark is called good diquark. Our main subject is to check if a lattice QCD simulation with 2 flavor Wilson fermions actually supports this statement. For this objective, we calculate diquark mass diference between good diquark and other diquarks and also analyze density distribution of diquarks through calculation of density-density correlators.

Speaker: Mr Ryutaro Fukuda (University of Tokyo, RIKEN BNL Research Center)

Slides fukuda_talk.pdf

Hadron Structure

Convener: Dr Jeremy Green (Institut für Kernphysik, Johannes Gutenberg-Universität Mainz)

18 The Calculation of Parton Distributions from Lattice QCD

Although parton distribution functions are the fundamental objects describing the inner structure of hadrons, they were so far not calculated from first principles. In the past, lattice QCD has successfully been employed for the computation of hadronic spectra and form factors. Yet calculations of quark distributions are still missing, since they are given by light-cone correlation functions and light-like distances are not accessible on an Euclidean lattice. This could possibly be overcome by a recent proposal which allows the light-cone distributions to be extracted from purely spatial correlations, being thus accessible to lattice methods. In order to test the feasibility of this method, we present the latest results of our effort to perform a lattice calculation of the non-singlet combination for the momentum, helicity and transversity distributions of the nucleon using twisted mass fermions. We will also give first results for the application of a newly proposed momentum improved smearing, which has the potential to reach higher nucleon momenta as required for a save matching procedure to the physical distribution functions.

Speaker: Dr Christian Wiese (NIC - DESY Zeuthen)

Slides wiese_lattice.pdf

19 Proton spin decomposition and its perturbative renormalization

I shall report on the progress of the proton spin decomposition based on Ji’s scheme and also the necessary perturbative calculation, to convert them from the lattice regularization to MS-bar scheme at 2 GeV.

Speaker: Dr YIBO Yang (university of Kentucky)

Slides lat_2016_short.pdf

20 Quark orbital dynamics in the nucleon - from Ji to Jaffe-Manohar orbital angular momentum

Quark orbital angular momentum (OAM) in the nucleon can be evaluated directly by employing a Wigner function embodying the simultaneous distribution of parton transverse position and momentum. This distribution can be accessed via a generalization of the nucleon matrix elements of quark bilocal operators which have been used previously in the lattice evaluation of transverse momentum dependent parton distributions (TMDs). By supplementing these matrix elements with a nonzero momentum transfer, mixed transverse position and momentum information is generated. In the quark bilocal operators, a gauge connection between the quarks must be specified; a staple-shaped gauge link path, as used in TMD calculations, yields Jaffe-Manohar OAM, whereas a straight path yields Ji OAM. A lattice calculation at a pion mass of 518 MeV is presented which demonstrates that the difference between Ji and Jaffe-Manohar OAM can be clearly resolved. The obtained Ji OAM is confronted with traditional evaluations utilizing Ji's sum rule. Jaffe-Manohar OAM is enhanced in magnitude compared to Ji OAM.

Speaker: Michael Engelhardt (New Mexico State University)

Slides talk.pdf

21 Nucleon spin and quark content at the physical point

The quark contributions to the spin and mass of the nucleon are computed using $N_f=2$ twisted mass fermions with a physical value of the pion mass. We use improved methods to obtain accurate results for the disconnected contributions involved in the evaluation of the axial charge and quark momentum fraction as well as the light, the strange and the charm $\sigma$-terms.

Speaker: Prof. Constantia Alexandrou (University of Cyprus and The Cyprus Institute)

Slides talk.pdf

22 Transverse spin densities of octet baryons

Fourier transforms of electromagnetic form factors provide valuable insights into the spatial distribution of quarks/charge within a hadron. When combined with form factors arising from non-forward matrix elements of the tensor operator, we are able to unlock fascinating information into the distribution of transversely polarised/unpolarised quarks within a transversely polarised/unpolarised hadron. Here we present results from the QCDSF collaboration for simulations in Nf=2+1 QCD for the form factors of the octet baryons and their resulting transverse spin densities. Particular attention is paid to SU(3) flavour breaking effects in the octet baryons as we move away from the SU(3)-symmetric point towards the physical point.

Speaker: Dr James Zanotti (University of Adelaide)

Slides Zanotti.pdf

23 Constructing Nucleon Operators on a Lattice for Form Factors with High Momentum Transfer

In typical nucleon structure calculations on a lattice, the interpolating fields are optimized to overlap with the nucleon ground state at rest, which in practice limits the momentum transfer in form factors to $Q^2\le 1\,GeV^2$. There is great interest in studying nucleon form factors up to few tens of GeV^2. New experiments at the JLab 12-GeV upgrade will measure nucleon form factors with momentum transfers up to $18\,GeV^2$ in an attempt to reach the regime of perturbative QCD scaling and investigate further the pattern in the GE/GM ratio in the proton. With current lattice QCD techniques, one can achieve momenta of several $GeV^2$ without risk of overwhelming discretization effects. In a boosted nucleon, however, excited state admixtures will become even more problematic to control than at rest, and will require computing nucleon correlators to high statistical precision. I will present some initial results from a lattice study of nucleon structure optimized for boosted nucleon initial and final states with the method recently adopted by the Regensburg collaboration. These methods will also be essential for the recently proposed novel method to compute parton distributions directly on a lattice.

Speaker: Sergey Syritsyn (Jefferson Lab)

Slides syritsyn-latt2016.pdf

Nonzero Temperature and Density

Convener: Dr Gergely Endrodi (University of Frankfurt)

24 Thermodynamics with physical mass staggered quarks

Finite temperature lattice QCD is investigated with four flavor physical mass staggered quarks using lattices upto N_t=20. Results for the equation of state and the low-lying modes of the Dirac-operator are presented with a focus on lattice artefacts.

Speaker: Kalman Szabo (U Wuppertal, FZ Juelich)

Slides sth16.pdf

25 Thermodynamics with continuum extrapolated overlap fermions

We study the QCD transition with dynamical overlap fermions. A continuum extrapolation is carried out using lattices up to N_t=12. We use a fixed topology approach and study its effect on our observables.

Speaker: Prof. Sandor Katz Katz (Eotvos University, Budapest)

Slides l16_katz.pdf

26 Strangeness at finite temperature

We give a lattice-based description of QCD thermodynamics in the hadronic phase from staggered simulations of up to $N_t=16$. Using generalized quark number susceptibilities we obtain the free energy in various strangeness sectors and compare it with the expectations from the hadron resonance gas model. We use the findings to disambiguate between various spectrum tables. Thus we constrain the abundance of strange mesons and baryons using finite temperature data

Speaker: Dr Szabolcs Borsanyi (University of Wuppertal)

Slides borsanyi.pdf

27 Continuum limit and universality of the Columbia plot

In its lower left corner, the Columbia plot indicates a first-order finite-temperature phase transition, which turns into a crossover as the quark masses increase. The locus of quark masses giving a second-order transition is a feature of continuum QCD, and should be recovered with any fermion discretization. However, numerical evidence has been accumulating, disfavoring universality. We explore this puzzle with 4 degenerate flavors of staggered fermions, thus avoiding any potential problem associated with rooting.

Speaker: Dr Philippe de Forcrand (ETH Zurich & CERN)

28 Critical endline of the finite temperature phase transition for 2+1 flavor QCD around the SU(3)-flavor symmetric point

We investigate the critical endline of the finite temperature phase transition of QCD around the SU(3)-flavor symmetric point at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and non-perturbatively $O(a)$-improved Wilson-clover fermion action. The critical endline is determined by using the intersection point of kurtosis, employing the multi-parameter, multi-ensemble reweighting method to calculate observables off the SU(3)-symmetric point, at the temporal size $N_{\rm T}$=6 and lattice spacing as low as $a \approx 0.19$ fm. We confirm that the slope of the critical endline takes the value of $-2$, and find that the second derivative is positive, at the SU(3)-flavor symmetric point on the Columbia plot parametrized with the strange quark mass $m_s$ and degenerated up-down quark mass $m_{\rm l}$.

Speaker: Dr Yoshifumi Nakamura (RIKEN)

Slides nakamura_20160725.pdf

29 New results for QCD at non-vanishing chemical potentials from Taylor expansion

We present recent results for QCD at non-vanishing chemical potentials for baryon number, electric charge and strangeness. The results are obtained from Taylor expanding the QCD partition function up to sixth order in these potentials. The numerical simulations for two light and one strange quark have been carried out on the basis of the Highly Improved Staggered Quark (HISQ) discretization scheme at lattice spacings which in the vicinity of the chiral transition temperature correspond to temporal extents of Nt = 6, 8 and 12, and at mass values which correspond to a physical Kaon mass and pion Goldstone masses around the physical value of 140 MeV. The results on, for instance, the equation of state are obtained as function of the three different chemical potentials and can thus also easily be adjusted to experimental conditions met in heavy ion colliders.

Speaker: Edwin Laermann (Bielefeld University)

Slides LaermannLat16.pdf

Physics Beyond the Standard Model

Convener: Prof. Benjamin Svetitsky (Tel Aviv University)

30 The scalar sector of $SU(2)$ gauge theory with $N_F=2$ fundamental flavours

We present a non perturbative study of SU(2) gauge theory with two fundamental Dirac flavours. This theory provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics. After reviewing our findings for the Goldstone bosons and spin-1 spectrum, we present our new results for the sigma and eta states. We evaluate the relevant disconnected contributions and obtain benchmark results that are crucial input for model building.

Speaker: Dr vincent Drach (CERN)

Slides lattice2016_drach.pdf

31 Infrared properties of a prototype pNGB model for beyond-SM physics

We construct a prototype BSM model where the Higgs boson is a pseudo Nambu-Goldstone boson by combining 4 light (massless) flavors and 8 heavy flavors. In the infrared, the SU(4) chiral symmetry is spontaneously broken , while in the ultraviolet it exhibits the properties of the $N_f=12$ conformal fixed point. The running coupling of this system ``walks" and the energy range of walking can be tuned by the mass of the heavy flavors. At the same time, renormalization group considerations predict the spectrum of such a system to show hyperscaling i.e. hadron masses in units of $F_\pi$ are independent of the heavy mass. Hyperscaling is present for bound states made-up of light, heavy, or heavy and light flavors. This observation is supported by numerical observations and makes the model strongly predictive.

Speaker: Prof. Anna Hasenfratz (University of Colorado)

Slides Lattice2016.pdf

32 Spectrum of a prototype model with the Higgs as pNGB

We present our results for the spectrum and other observables of an SU(3) gauge theory with 4 light fermions and 8 fermions of heavier mass, built on an IR fixed point. Our numerical data validate hyperscaling and, while our model does not presume to be a complete theory of EW symmetry breaking, it exhibits many of the features that would be expected of a realistic theory where the Higgs emerges as a pNGB.

Speaker: Prof. Claudio Rebbi (Boston University)

Slides rebbi_lat16.pdf

33 Near-conformal composite Higgs or PNGB with partial compositeness?

Based on recent analysis of the LatHC collaboration I will review critical features of a minimal composite Higgs model close to the conformal window. Challenging problems of the near-conformal paradigm will be compared with PNGB based partial compositeness.

Speaker: Prof. Julius Kuti (U.C. San Diego)

Slides jkLattice2016.pdf

34 Spectrum and mass anomalous dimension of SU(2) gauge theories with fermions in the adjoint representation: from $N_f=1/2$ to $N_f=2$

In this work I will summarize our results concerning the spectrum and mass anomalous dimension of SU(2) gauge theories with a different number of fermions in the adjoint representation, where each Majorana fermion corresponds effectively to half a Dirac flavour $N_f$. The most relevant examples for the extensions of the standard model are supersymmetric Yang-Mills theory ($N_f=1/2$) and minimal walking technicolour ($N_f=2$). In addition to these theories I will also consider the cases of $N_f=1$ and $N_f=3/2$. The results will contain the particle spectrum of glueballs, triplet and singlet mesons, and possible fractionally charged spin half particles. In addition I will discuss our recent results for the mass anomalous dimension.

Speaker: Dr Georg Bergner (AEC ITP University of Bern)

Slides 16Lattice.pdf

35 Large mass hierarchies from strongly-coupled dynamics

Motivated by tentative signals of new physics at the LHC, which seems to imply the presence of large mass hierarchies, we investigate the theoretical possibility that these could arise dynamically in new strongly-coupled gauge theories extending the standard model of particle physics. To this purpose, we study lattice data on non-Abelian gauge theories in the (near-)conformal regime—specifically, $\mathrm{SU}(2)$ with $N_{\mathrm{f}}=1$ and $2$ dynamical fermion flavours in the adjoint representation. We focus our attention on the ratio $R$ between the masses of the lightest spin-2 and spin-0 resonances, and draw comparisons with a simple toy model in the context of gauge/gravity dualities. For models in which large anomalous dimensions arise dynamically, we show indications that this mass ratio can be large, with $R > 5$. Moreover, our results suggest that $R$ might be related to universal properties of the IR fixed point. Our findings provide an interesting step towards understanding large mass ratios in the non-perturbative regime of quantum field theories with (near) IR conformal behaviour.

Speaker: Dr Ed Bennett (Swansea University)

Slides ejb-web.pdf

Theoretical Developments

Convener: Prof. Margarita Garcia-Perez (Instituto de Fisica Teorica UAM-CSIC)

36 The Slab Method to Measure the Topological Susceptibility

In simulations of a model with topological sectors, algorithms which proceed in small update steps tend to get stuck in one sector, especially on fine lattices. This distorts the numerical results; in particular it is not straightforward to measure the topological susceptibility chi_t. Here we test a method to measure chi_t even if configurations from only one sector are available. It is based on the topological charges in sub-volumes, which we denote as ''slabs''. Under suitable circumstances, this enables the evaluation of chi_t, as we demonstrate with numerical data for non-linear sigma-models and 2-flavor QCD.

Speaker: Dr Wolfgang Bietenholz (UNAM, Mexico)

Slides slab.pdf

37 Determination of topological charge following several definitions

On the lattice, many definitions of the topological charge $Q$ coexist, and can give very different numbers on a given configuration. Those definitions will only converge when one takes the continuum limit of the moments $\langle Q^n\rangle$ (provided that $Q$ has been correctly renormalised). Additionally, other complications arise when one wants to study the mass dependence of the topological susceptibility, because of the mixing of the two operators under renormalisation. It is therefore unclear to which extent each definition of $Q$ is compatible with each definition of the masses. Here we will present the results of some tests following various choices of definition. In a second part, we will discuss the potential consequences of that ambiguity on the discarding of $m_u=0$ as a solution to the strong $CP$ problem.

Speaker: Dr Julien Frison (KEK Theory Center)

Slides slides.pdf

38 Fermion bags, topology and index theorems

In this talk we argue that the fermion bag formulation extends the concepts of topology and index theorems associated with non-Abelian gauge theories, to simple lattice fermion field theories. Through such a connection we learn that fermion masses can arise in at least two different ways:(1) a conventional way where some lattice symmetry of the action is spontaneously, explicitly or anomalously broken and (2) an unconventional way where all lattice symmetries are preserved. We argue for these two scenarios by considering simple examples of lattice field theories formulated with staggered fermions.

Speaker: Prof. Shailesh Chandrasekharan (Duke University)

Slides Presentation at the Conference

39 Lattice QCD on non-orientable manifolds - part I

A common problem in lattice QCD simulations on the torus is the extremely long autocorrelation time of the topological charge, when one approaches the continuum limit. The reason is the suppressed tunneling between topological sectors. The problem can be addressed by replacing the torus with a different manifold. Here we propose to use a non-orientable manifold, and show how to define and simulate lattice QCD on it. Part I focuses on the motivation and general introduction of our construction.

Speaker: Dr Simon Mages (Forschungszentrum Jülich)

Slides lat16_mages.pdf

40 Lattice QCD on non-orientable manifolds - part II

A common problem in lattice QCD simulations on the torus is the extremely long autocorrelation time of the topological charge, when one approaches the continuum limit. The reason is the suppressed tunneling between topological sectors. The problem can be addressed by replacing the torus with a different manifold. Here we propose to use a non-orientable manifold, and show how to define and simulate lattice QCD on it. Part II focuses on special issues like the implementation of fermions on a non-orientable manifold.

Speaker: Dr Balint Toth (Bergische Universität Wuppertal)

Slides tothb_talk.pdf

41 Lattice QCD simulation of the Berry curvature

The Berry curvature is a fundamental concept describing topological order of quantum systems. While it can be analytically tractable in non-interacting systems, numerical simulations are necessary in interacting systems. We present a formulation to calculate the Berry curvature in lattice QCD.

Speaker: Arata Yamamoto (University of Tokyo)

Slides Yamamoto.pdf

4:15 PM Coffee Break

Hadron Spectroscopy and Interactions

Convener: Prof. Christine Davies (University of Glasgow)

42 Importance of closed quark loops for lattice QCD studies of tetraquarks

To investigate the light scalar tetraquark candidate $a_0(980)$ (quantum numbers $J^P=0^+$), a correlation matrix including a variety of two- and four-quark interpolating operators has to be computed. We discuss efficient techniques to compute the elements of this correlation matrix. In particular we present numerical results for diagrams with closed quark loops and present evidence that such diagrams are not negligible, i.e. that their contribution is essential to obtain physically meaningful results.

Speaker: Mr Joshua Berlin (University of Frankfurt)

Slides JBerlin_Lattice16.pdf

43 Using a new analysis method to extract excited states in the scalar meson sector

We present an alternative method to the Generalized Eigenvalue Problem (GEVP) for extracting excited states. The method is based on statistically sampling the space of possible set of parameters according to the $\chi^2$-value of each set of values. This method is particularly suited when one has noisy data as is the case for some correlators at large times such as in the scalar light qqbar channel. We will apply this method to the analysis of the $J^P = 0^+$ channels used in the search for the $a_0$ particle and compare the results to the standard GEVP approach, pointing out advantages and disadvantages of the method compare to the GEVP approach.

Speaker: Dr Jacob Finkenrath (german)

Slides slides_lat16.pdf

44 Computing the static potential using non-string-like trial states

We present a method for computing the static quark-antiquark potential, which is not based on Wilson loops, but where the trial states are formed by eigenvector components of the covariant Laplace operator. We have tested this method in SU(2) Yang-Mills theory and obtained results with statistical errors of similar magnitude compared to a standard Wilson loop computation. The runtime of the method is, however, significantly smaller, when computing the static potential not only for on-axis, but also for many off-axis quark-antiquark separations, i.e. when a fine spatial resolution is required.

Speaker: Mr Tobias Neitzel (Goethe University Frankfurt)

Slides Vortrag.pdf

45 Testing the hadro-quarkonium model on the lattice

Recently the LHCb experiment found evidence for the existence of two exotic resonances consisting of $c\bar{c}uud$ quarks. Among the possible interpretations there is the hadro-charmonium model, in which charmonium is bound "within" a hadron. We test this idea on CLS $n_f$=2+1 lattices using the static formulation for the heavy quarks. We find that the static potential is modified by the presence of a hadron. It becomes more attractive and the effect is of the order of few MeV.

Speaker: Prof. Francesco Knechtli (University of Wuppertal)

Slides hadroquark_lat16.pdf

46 Hindered M1 Radiative Decays

Throughout the literature, phenomenological models have been unsuccessful in pinning down the heavy quarkonia hindered M1 radiative transitions (i.e., those radiative transitions between states with different principal quantum numbers that require one of the quarks to flip-spin) and yield predictions that are spread over a vast range. In this talk, we will learn how to accurately and precisely predict these classes of decays by utilising lattice NRQCD, compare to the phenomenological calculations, and then show how this work is relevant for the experimental hyperfine splitting.

Speaker: Mr Ciaran Hughes (University of Cambridge)

Slides CH_LAT2016.pdf

47 Towards radiative transitions in charmonium

We present preliminary calculations towards radiative transitions in charmonium using Nf = 2+1 dynamical ensembles generated by the Hadron Spectrum Collaboration. A crucial ingredient in this work is the use of variationally optimised interpolating operators which allow for a reliable determination of the three-point correlation functions needed. Using these operators, we perform first calculations of relevant three-point correlation functions before discussing future directions"

Speaker: Mr Cian O'Hara (Trinity College Dublin)

Slides Slides.pdf

Hadron Structure

Convener: Dr Benoit Blossier (CNRS)

48 Hadron Matrix Elements and the Feynman-Hellman Theorem

Motivated by the Feynman-Hellman Theorem, we develop an improved method for computing matrix elements of external currents utilizing only two-point correlation functions. The contamination from excited states is shown to be Euclidean-time dependent allowing for a significantly improved ability to reliably determine and control the systematics. We demonstrate the utility of our method with a calculation of the nucleon axial-charge, performed at a single lattice spacing and a moderate unphysical pion mass. The Feynman-Hellman Theorem can be derived from the long Euclidean-time limit of correlation functions determined with functional derivatives of the partition function. This elucidates the generic applicability of our new method: one can determine matrix elements of any external current by computing only two-point correlation functions, including non-zero momentum transfer and flavor-changing matrix elements.

Speaker: Andre Walker-Loud (LBNL)

Slides walker-loud_fht.pdf

49 Hadron Structure from the Feynman-Hellmann Theorem

Although hadron structure calculations in lattice QCD have improved greatly in recent years, many problems still remain. Various techniques for determining fermion line disconnected contributions to matrix elements have produced exciting and promising results, but rely on complicated analyses. Additionally, calculations of electromagnetic form factors at high momentum transfers remain limited by low signal-to-noise ratios. In this talk we present results from Feynman-Hellmann motivated approaches to determinations of these quantities. We find disconnected contributions to $\Delta \Sigma$ consistent with stochastic calculations, and are able to access significantly higher momentum transfers for electromagnetic form factors than have previously been feasible. In conjunction with experimental data, these results may reveal interesting information regarding the possibility of a zero crossing in the ratio of electric and magnetic form factors in the nucleon.

Speaker: Mr Alexander Chambers (University of Adelaide)

Slides achambers.pdf

50 Nucleon structure from 2+1-flavor dynamical DWF ensembles

Nucleon isovector vector- and axialvector-current form factors and some low moments of isovector structure functions will be reported with improved statistics from four recent RBC+UKQCD 2+1-flavor dynamical drain-wall fermions ensembles: Iwasaki gauge 24^3x64 at 1.78-GeV momentum cut off and pion mass of 432 ans 330 MeV and Iwasaki times DSDR gauge 32^3x64 at 1.38 GeV momentum cut off and pion mass of 250 and 172 MeV.

Speaker: Dr Shigemi Ohta (KEK)

Slides 0.pdf

51 Nucleon Matrix Elements at Physical Point and Cost Comparison

I shall report on calculations of isovector matrix elements of the nucleon, such as $g_A, g_s$, and $\langle x \rangle$ on the $48^3 \times 96$ lattice with pion mass at 139 MeV and lattice size of 5.5 fm. We employ overlap valence fermion on the 2+1 flavor DWF configurations for the calculation. Also reported will be the strange quark momentum fraction and its magnetic moment from this lattice. A comparison of the cost of such calculations with those of the twisted mass fermion, clover fermion, and domain wall fermion on similar lattices and quark masses will be made for the calculation of the nucleon mass and the three-point functions of both the connected and disconnected insertions.

Speaker: Prof. Keh-Fei Liu (University of Kentucky)

Slides Overlap_CI_48_cost_comparison.pdf

52 Light-cone distribution amplitudes of the baryon octet

We present results of the first ab initio lattice QCD calculation of the normalization constants and first moments of the leading twist distribution amplitudes of the full baryon octet, corresponding to the small transverse distance limit of the associated S-wave light-cone wave functions. The P-wave (higher twist) normalization constants are evaluated as well. The calculation is done using $N_f=2+1$ flavors of dynamical (clover) fermions on lattices of different volumes and pion masses down to 222 MeV. Significant SU(3) flavor symmetry violation effects in the shape of the distribution amplitudes are observed.

Speaker: Mr Fabian Hutzler (University Regensburg)

Slides Lattice16_Hutzler_BDA.pdf

53 Renormalization of three-quark operators for baryon distribution amplitudes

Octet baryon distribution amplitudes are non-perturbative objects of phenomenological interest parametrizing the momentum distribution within the corresponding Fock states. Their normalization and their moments can be calculated using lattice QCD, and such results require renormalization. However, the MS-bar scheme, i.e., the renormalization scheme used in phenomenological applications, necessitates a perturbative approach in non-integer spacetime dimension and is therefore not well suited for lattice calculations. Instead, we renormalize the lattice results non-perturbatively in a RI'/SMOM scheme and carry out the conversion to the MS-bar scheme in continuum perturbation theory. Using group theoretical and symmetry considerations we have constructed optimized three-quark operator bases for the renormalization procedure in order to minimize mixing.

Speaker: Mr Michael Gruber (RQCD collaboration)

Slides Michael_Gruber_Lattice_25.07.2016.pdf

Nonzero Temperature and Density

Convener: Prof. Kazuyuki Kanaya (CiRfSE, Univ. Tsukuba)

54 The QCD deconfinement critical point as a function of N_t with N_f=2 flavours of unimproved Wilson fermions

QCD at zero baryon density in the limit of infinite quark mass undergoes a first order deconfinement phase transition at a critical temperature T_c corresponding to the breaking of the global centre symmetry. In the presence of dynamical quarks the global centre symmetry is explicitly broken. Lowering the quark mass the first order phase transition weakens and terminates in a second order Z(2) point. Beyond this line confined and deconfined regions are analytically connected by a crossover transition. As the continuum limit is approached (i.e. the lattice spacing is decreased) the region of first order transitions expands towards lower masses. We study the deconfinement critical point with standard Wilson fermions and N_f=2 flavours. Therefore we simulate several kappa values on N_t=8 and various aspect ratios in order to extrapolate to the thermodynamic limit, applying finite size scaling. We estimate if and when a continuuum extrapolation is possible.

Speaker: Mr Christopher Czaban (Goethe University Frankfurt am Main)

Slides christopher_czaban_presentation_lattice2016.pdf

55 Roberge-Weiss transition in Nf=2 QCD with staggered fermions and Nt=6

The QCD phase diagram at imaginary chemical potential exhibits a rich structure and studying it can constrain the phase diagram at real values of the chemical potential. Moreover, at imaginary chemical potential standard numeric techniques based on importance sampling can be applied, since no sign problem is present. In the last decade, a first understanding of the QCD phase diagram at imaginary chemical potential has been developed, but it is so far based on investigations on coarse lattices ($N_t=4,\;a=0.3$ fm). Considering the $N_f=2$ case, at the Roberge-Weiss critical value of the imaginary chemical potential, the chiral/deconfinement transition is first order for light/heavy quark masses and second order for intermediate values of the mass: there are then two tricritical masses, whose position strongly depends on the lattice spacing and on the discretisation. On $N_t=4$, we have the chiral $m_{\pi}^{\mbox{tric.}}\simeq400$ MeV with unimproved staggered fermions and $m_{\pi}^{\mbox{tric.}}\simeq900$ MeV with unimproved pure Wilson fermions. Employing finite size scaling we investigate the change of this tricritical point between $N_t=4$ and $N_t=6$ as well as between Wilson and staggered discretisations.

Speaker: Mr Alessandro Sciarra (Goethe Universität)

56 The chiral phase transition from non-integer flavour numbers with staggered fermions

The attempt at clarifying the order of the thermal transition in the chiral limit of QCD at zero chemical potential, with two dynamical flavours of quarks, by progressively decreasing the simulated pion mass has proven to be inconclusive because of the increasing costs of the simulations as the pion mass is lowered. An alternative way to approach this question is to consider the path integral as a function of continuous N_f . If the transition is first order for N_f ≳ 3 , a second order transition for N_f = 2 requires a tricritical point in between. The simulation of non-integer numbers of fermion flavours is easily achievable within the staggered fermion discretization. First simulations at μ = 0 and N_f = 2.8, 2.6, 2.4, 2.2 , on coarse N_τ = 4 lattices, show a continuous variation of the critical mass mapping out a critical line in the m − N_f plane.

Speaker: Ms Francesca Cuteri (Goethe University - Frankfurt)

Slides talklattice2016_cuteri.pdf

57 Roberge-Weiss periodicity and confinement-deconfinement transition

We propose a new determination of the confinement-deconfinement transition by using the imaginary chemical potential. The imaginary chemical potential can be interpreted as the Aharonov-Bohm phase and then an analogy of the topological-order suggests that the Roberge-Weiss endpoint would define the deconfinement temperature. Based on the topological property, we can construct a new quantity which describes the confinement-deconfinement transition. This quantity is defined as the integral of the quark number susceptibility along the closed loop of $\theta$ where $\theta$ is the dimensionless imaginary chemical potential. Expected behavior of it at finite temperature is discussed and its asymptotic behaviors are shown.

Speaker: Dr Kouji Kashiwa (Yukawa Institute for Theoretical Physics, Kyoto University)

Slides 20160725_Lattice.pdf

58 The Roberge-Weiss endpoint in $N_f=2+1$ QCD at the physical point

In this talk I will report on our recent results about the determination of the position and the nature of the Roberge-Weiss endpoint. Our study is performed in $N_f=2+1$ QCD, with physical quark masses, making use of stout-improved staggered fermions and of the tree level Symanzik improvement for the gauge action. We study the theory at 4 different lattice spacings, corresponding to $N_t=4,6,8$ and $10$, and at different spatial sizes. The finite size scaling analysis performed on $N_t=4$ and $6$ lattices indicates that the Roberge-Weiss transition at the endpoint is of the 2nd order kind, in the 3D Ising universality class, while the continuum limit of the critical temperature is found to be $T_{RW}=208(5)$ MeV.

Speaker: Mr Michele Mesiti (University of Pisa and INFN - Sezione di Pisa)

Slides lattice2016_Michele_Mesiti.pdf

59 Locating the critical end point of QCD

I will give an overview on our recent results for the phase diagram of QCD with Nf=2+1 and Nf=2+1+1 flavors. We use a combination of lattice and Dyson-Schwinger methods to determine the chiral and deconfinement order parameters at finite temperature and chemical potential. In a recent exploratory study we also give a first estimate on the influence of baryon effects on the location of the critical end-point. As a result we find a critical end-point at large chemical potential in the vicinity of the chiral critical line extrapolated from lattice QCD.

Speaker: Prof. Christian Fischer (JLU Giessen)

Slides Lattice16_Fischer_v3.pdf

Physics Beyond the Standard Model

Convener: Prof. Julius Kuti (U.C. San Diego)

60 Quark Chromoelectric Dipole Moment Contribution to the Neutron Electric Dipole Moment

The quark chromo-electric dipole moment operator and the pseudo-scalar fermion bilinear with which it mixes under renormalization can both be included in a calculation of the electromagnetic form factor of the nucleon using the Schwinger source method. A preliminary calculation of these operators using clover quarks on HISQ lattices generated by MILC collaboration will be presented showing the quality of the signal in the correlators necessary for calculating the neutron electric dipole moment.

Speaker: Dr Tanmoy Bhattacharya (Los Alamos National Laboratory)

Slides Bhattacharya.pdf

61 Effective action for pions and a dilatonic meson - foundations

Recent simulations suggest the existence of a very light singlet scalar in QCD-like theories that may be lying just outside the conformal window. Assuming that the lightness of this scalar can be explained by an approximate dilatation symmetry, we develop an effective field theory framework for both the pions and this light scalar, the "dilatonic meson." We argue that a power counting exists that puts this effective field theory on a systematic footing.

Speaker: Dr Yigal Shamir (Tel Aviv University)

Slides Latt16_YS.pdf

62 Effective action for pions and a dilatonic meson - results

We consider applications of a recently developed effective field theory for a dilatonic meson and pions. We contrast the leading-order behavior of masses with that in a theory with only pions, comment on next-to-leading order, and argue that the effective theory breaks down at the sill of the conformal window, as it should.

Speaker: Prof. Maarten Golterman (San Francisco State University)

Slides golterman_lattice16.pdf

63 Asymptotically safe gauge-Yukawa theories and functional renormalisation group

Recently, new four-dimensional (gauge-Yukawa) theories have been discovered which display exact interacting fixed points at highest energies. In a regime where asymptotic freedom is lost, these novel types of theories develop an asymptotically safe UV fixed point, strictly controlled by perturbation theory. In this talk, we extend these studies to include couplings with non-vanishing canonical mass dimension. Using the method of functional renormalisation, we determine the full fixed point potential including higher order invariants of e.g. the scalar and fermionic fields. We also compute the universal scaling exponents and establish consistency of the theory beyond the restriction to classically marginal operators.

Speaker: Ms Tugba Buyukbese (University of Sussex)

Slides Lattice2016.pdf

64 Interacting ultraviolet completions of four-dimensional gauge theories

We will discuss some of the recent developments in understanding ultraviolet completions of gauge-Yukawa theories beyond traditional asymptotic freedom.

Speaker: Mr Andrew Bond (University of Sussex)

Slides Lattice-Jul-16.pdf

65 Finite Size Scaling of the Higgs-Yukawa Model near the Gaussian Fixed Point

We study the scaling property of Higgs-Yukawa models. Using the technique of Finite-Size Scaling, we are able to derive formulae to describe the behaviour of the observables near the Gaussian fixed point. The renormalisation procedure is discussed in this talk. A feasibility study of our strategy is performed for pure scalar theory. In addition, we test the formulae with lattice data obtained in the weak-coupling regime for the Higgs-Yukawa model. These formulae can be used to investigate the universality classes of the observed phase transitions, and thus play an essential role in further investigations of Higgs-Yukawa models.

Speaker: David Y.-J. Chu (Department of Electrophysics, National Chaio Tung University)

Slides Chu_latt2016_PlotFix.pdf

Standard Model Parameters and Renormalization

Convener: Dr Krzysztof Cichy (Goethe-University Frankfurt am Main)

66 On the accuracy of perturbation theory in QCD

A collaborative effort to determine the $\Lambda$-parameter in 3-flavour QCD by the ALPHA collaboration is currently being finalized. The strategy involves 2 finite volume schemes for the coupling, both defined with Schroedinger functional (SF) boundary conditions. I here discuss the scale evolution from an intermediate scale $1/L_0$ of about 4 GeV to scales of O(100) GeV using the traditional SF coupling and a 1-parameter family of close relatives. Our precise continuum extrapolated data allows for stringent tests of perturbation theory, which is then used to extract $L_0*\Lambda$ with an error below 3 per cent. To quote such a small error with confidence, non-perturbative data is required around alpha_s = 0.1. In particular, we have evidence that the apparent precision reached with data around alpha_s = 0.2 can be misleading. (cf. related talks by A. Ramos and R. Sommer)

Speaker: Prof. Stefan Sint (Trinity College Dublin)

Slides lat16.pdf

67 The Nf=3 gradient flow coupling running from 4GeV to 200MeV

A fundamental step in the ALPHA collaboration efforts to determine the fundamental parameters of $N_f=3$ QCD at the electroweak scale in terms of hadronic quantities is the connection of an intermediate scale $\sim 4{\rm GeV}$ with a hadronic scale. In this talk we will show that using the Gradient Flow running coupling this task can be achieved with a very high precision. Our analysis will pay special attention to the continuum limit of flow quantities and reach a precision below 2% in the scale factor for a change of the coupling from $g^2=13$ to $g^2=2.5$.

Speaker: Dr Alberto Ramos (CERN)

Slides lat16.pdf

68 Precision determination of the strong coupling at the electroweak scale

The ALPHA-collaboration computation of the three-flavor Lambda-parameter and the determination of $\alpha(m_Z)$ consists of the steps: Running from beyond the Z-mass to 4 GeV in the SF scheme, matching to the GF scheme, running from 4GeV to small energy in the GF scheme, determining the smallest energy scale ($\approx$ 200 MeV) in physical units with the help of the CLS simulations. We summarize the first steps and discuss the last one in detail. We then present our final result for $\Lambda_{\rm \overline{MS}}^{(3)}$ with its error budget. Finally, the connection of the three-flavor theory to the five-flavor $\alpha(m_Z)$ uses decoupling and high order perturbation theory in the $\rm \overline{MS}$ scheme.

Speaker: Prof. Rainer Sommer (NIC @ DESY)

Slides RS-lat16-fin.pdf

69 Determining $\alpha_s$ by using the gradient flow in the quenched theory

We present preliminary results to determine the strong coupling constant by using the gradient flow. Pure SU(3) gauge theory is studied. We carry out a direct analysis on very fine zero temperature lattices. In addition we attempt to move towards the perturbative regime by using step-scaling.

Speaker: Dr Eliana Lambrou (University of Wuppertal)

Slides Lambrou_Lattice16.pdf

70 Numerical determination of the $\Lambda$-parameter in SU(3) gauge theory from the twisted gradient flow coupling

We calculate the $\Lambda$-parameter in $\overline{\mathrm{MS}}$ scheme for SU(3) pure gauge theory with the twisted gradient flow method non-perturbatively. Using the Schrödinger functional scheme as an intermediate scheme, we numerically evaluate the $\Lambda$-parameter ratio $\frac{\Lambda_{\overline{\mathrm{MS}}}}{\Lambda_{\mathrm{TGF}}}=\frac{\Lambda_{\overline{\mathrm{MS}}}}{\Lambda_{\mathrm{SF}}}\cdot\frac{\Lambda_{\mathrm{SF}}}{\Lambda_{\mathrm{TGF}}}$. We also estimate $\Lambda_{\mathrm{TGF}}/\sqrt{\sigma}$ and $r_{0}\Lambda_{\mathrm{TGF}}$ from $a\sqrt{\sigma}$ and $a/r_{0}$ available in the literature. Our final values $\Lambda_{\overline{\mathrm{MS}}}/\sqrt{\sigma}$ and $r_{0}\Lambda_{\overline{\mathrm{MS}}}$ are consistent with the known results, which demonstrates the validity of the present method.

Speaker: Mr Ryoichiro Ueno (Graduate School of Science, Hiroshima University)

Slides Lattice2016_4_ueno.pdf

71 Running coupling from Wilson flow for three quark flavors

The running coupling constant $\alpha_s(Q^2)$ is computed from the Wilson flow for three quark flavors on multiple volumes and a wide range of lattice spacings, which allows for a continuum extrapolation. Of particular interest is the behavior at small $Q^2$ and the question of an infrared fixed point.

Speaker: Prof. Gerrit Schierholz (DESY)

Slides lat16.pdf

Theoretical Developments

Convener: Prof. Roberto Frezzotti (University of Rome Tor Vergata, Physics Department and INFN - Sezione di Roma Tor Vergata)

72 Beyond complex Langevin equations:positive representation of Feynman path integrals directly in the Minkowski time

A positive representation for an arbitrary complex, gaussian weight is derived and used to construct a statistical formulation of gaussian path integrals directly in the Minkowski time. The positivity of Minkowski weights is achieved by doubling the number of real variables. The continuum limit of the new representation exists only if some of the additional couplings tend to infinity and are tuned in a specific way. The construction is then successfully applied to three quantum mechanical examples including a particle in a constant magnetic field -- a simplest prototype of a Wilson line. Further generalizations are shortly discussed and an intriguing interpretation of new variables is alluded to.

Speaker: Jacek Wosiek (Jagellonian University)

Slides WosiekLattice2016.pdf

73 Phase structure analysis of CP(N-1) model using Tensor renormalization group

We investigate the phase structure of the lattice CP(N-1) model in two dimensions by using the tensor renormalization group (TRG) method. The TRG method has no sign problem even though the action is complex. We focus on the case N=2 and compare the numerical result of the TRG method with that of the strong-coupling analysis in the presence of the theta term.

Speaker: Mr Hikaru Kawauchi (Kanazawa University)

Slides LATTICE2016_kawauchi_final.pdf

74 The multi-flavor Schwinger model with chemical potential - Overcoming the sign problem with Matrix Product States

During recent years there has been quite some interest in applying Matrix Product States and more general tensor networks to lattice gauge theories in the Hamiltonian formulation. Previous work already demonstrated the power of this approach by computing the mass spectrum and thermal sates for the Schwinger model, and also real-time dynamics for abelian and non-abelian gauge models have been successfully addressed in the meantime. In this talk we present ground state calculations for the two-flavor Schwinger model with finite chemical potential using Matrix Product States. While the conventional Monte Carlo approach suffers from the sign problem, our numerical simulations with Matrix Product States reliably reproduce analytic results for the massless case by Narayanan [Phys. Rev. D 86, 125008 (2012)] and readily extend to the massive case, where no analytic prediction is available.

Speaker: Stefan Kühn (Max Planck Institute of Quantum Optics)

Slides Kuehn_Lattice2016.pdf

75 Diagrammatic Monte-Carlo simulations of the large N SU(N)xSU(N) principal chiral model based on the weak-coupling trans-series expansion

I present a Diagrammatic Monte-Carlo algorithm for the large N SU(N)xSU(N) principal chiral model, which stochastically samples planar Feynman diagrams of the lattice perturbation theory. The latter is constructed using the Cayley map from SU(N) group manifold to the space of Hermitian matrices. I demonstrate that the Jacobian of this map results in the massive bare lattice propagator with the mass proportional to the bare coupling. This bare mass term ensures that perturbative series are IR finite and do not have factorial divergences at high orders, which makes the series suitable for Monte-Carlo sampling and stochastic summation. On the other hand, since the bare mass is proportional to the coupling itself, the expansion is no longer an expansion in powers of coupling, but rather has the form of trans-series involving both powers and logs of coupling. I discuss possible resurgent structure of these trans-series, the strength of the sign problem in Monte-Carlo sampling, as well as the extension of the present approach to lattice gauge theory.

Speaker: Dr Pavel Buividovich (Regensburg University)

Slides Lattice2016Buividovich.pdf

76 New polynomially exact integration rules on U(N) and SU(N)

In lattice QFT, we are often presented with integrals over polynomials of coefficients of matrices in $U(N)$ or $SU(N)$ with respect to the Haar measure. In some physical situations, e.g., in presence of a chemical potential, these integrals are, however, numerically very difficult since they are highly oscillatory which manifests itself in form of the sign problem. In these cases, Monte Carlo methods often fail to be adequate, rendering such computations practically impossible. In this talk, we will propose a new class of polynomially exact integration rules on $U(N)$ and $SU(N)$ which are derived from polynomially exact rules on spheres. We will examine these quadrature rules and their efficiency at the example of a $0+1$ dimensional QCD for a non-zero quark mass and chemical potential. In particular, we will demonstrate the failure of Monte Carlo methods in such applications but that we can obtain arbitrary precision results using the new polynomially exact integration rules.

Speaker: Dr Tobias Hartung (King's College London)

Slides hartung_Lattice2016.pdf

77 How to make a quantum black hole with ultra-cold gases

We argue that a small, quantum black hole can be made from atoms and lasers. The holographic principle claims that the quantum gravitational systems, e.g. superstring theory, is equivalent to non-gravitational quantum systems, e,g. super Yang-Mills theory. Here the 'equivalence' means two theories cannot be distinguished even in principle. Therefore, if the holographic principle is true, then by engineering the non-gravitational systems by using an optical lattice, one can create actual quantum black holes. In this presentation, we consider the simplest example: the Sachdev-Ye-Kitaev (SYK) model. We design a an experimental scheme for creating the SYK model with use of ultra-cold fermionic atoms. This presentation is based on a paper "Creating and probing the Sachdev-Ye-Kitaev model with ultracold gases: Towards experimental studies of quantum gravity," arXiv:1606.02454 with Ippei Danshita (Yukawa Institute for Theoretical Physics, Kyoto University) and Masaki Tezuka (Deptartment of Physics, Kyoto University).

Speaker: Masanori Hanada (Kyoto U, Stanford U)

Slides EQG_LATTICE2016.pdf

Public Lecture: From the Origins of Mass to the Stability of Matter: Lattice QCD and Supercomputers

78 From the Origins of Mass to the Stability of Matter: Lattice QCD and Supercomputers

The origin of mass is mysterious. In our everyday experience, the mass of an object is the sum of the mass of its parts. However, in the world of subatomic particles such as quarks and gluons, this everyday assumption is no longer true and even very small mass differences can have cosmic consequences. After an introduction to the subatomic world and the mechanisms by which mass emerges, I will describe how supercomputers are being used to compute from first principles the interactions between elementary particles in order to reveal the origins of mass and to explain the stability of the matter which constitutes us and the visible universe. Tickets for this public lecture can be booked via Eventbrite http://latticeqcd.eventbrite.co.uk/ .

Speaker: Dr Laurent Lellouch (CNRS & Aix-Marseille U.)

Tuesday, July 26

Plenary Session

Convener: Prof. Constantia Alexandrou (University of Cyprus and The Cyprus Institute)

79 Nuclear Physics

Lattice QCD is making good progress toward calculating the structure and properties of light nuclei and the forces between nucleons. These calculations will ultimately refine the nuclear forces, particularly in the three- and four-nucleon sector and the short-distance interactions of nucleons with electroweak currents, and allow for a reduction of uncertainties in nuclear many-body calculations of nuclei and their reactions. After highlighting their importance, particularly to the Nuclear Physics and High-Energy Physics experimental programs, I will discuss the progress that has been made toward achieving these goals and the challenges that remain.

Speaker: Prof. Martin Savage (Institute for Nuclear Theory)

Slides Savage_Lattice_2016_v1p2_pdf.pdf

80 New simulation strategies for lattice QCD

Despite the numerous successful applications of lattice QCD in nuclear and particle theory, fundamental algorithmic challenges remain. Among those, relevant for numerical studies of QCD on a space time torus, is topological freezing--a form of critical slowing down, which becomes particularly severe for lattice spacing less than 0.05 fm. In this talk, I will highlight several recently proposed simulation strategies for ameliorating the problem of topological freezing, discussing both the advantages and disadvantages of such approaches. Then, I will turn focus toward strategies for addressing critical slowing down in a more general context.

Speaker: Dr Michael Endres (MIT)

Slides Endres-plenary-repaired.pdf https://www.dropbox.com/s/n72uryzwhx8sn90/Endres-plenary.pdf?dl=0

81 Tensor networks

In this talk, I will review the recent progress of tensor network approaches; Hamiltonian/Hilbert-space approach and Lagrangian/path-integral approach, whose striking feature is free of the sign problem. As examples, I will show some results of CP(N-1) model including theta-term and other models. Finally, I will address outstanding problems and discuss future prospects.

Speaker: Dr Shinji Takeda (Kanazawa University)

Slides 20160726_takeda.pdf

10:45 AM Coffee

Plenary Session

Convener: Dr James Zanotti (University of Adelaide)

82 Hadron Structure

Recent calculations of hadron structure observables and related technical and theoretical advances are reviewed. A wealth of information on the properties of hadrons can be provided by lattice methods such as their wavefunctions, response to electromagnetic, weak or beyond the Standard Model probes and their internal dynamics in terms of the contributions from quarks and gluons. Progress in the evaluation of benchmark quantities which are well determined from experiment will be discussed, along with the control of systematics before highlighting recent calculations of more challenging and less well known observables.

Speaker: Dr Sara Collins (University of Regensburg)

Slides talk.pdf

83 From C to Parton Sea: Bjorken-x dependence of the PDFs

Studying the structure of nucleons is not only important to understanding the strong interactions of quarks and gluons, but also to improving the precision of new-physics searches. Since a broad class of experiments, including the LHC and dark-matter detection, require Standard-Model backgrounds with parton distribution functions (PDFs) as inputs for disentangling SM contributions from potential new physics. For a long time, lattice calculations of the PDFs (as well as many hadron structures) has been limited to the first few moments. In this talk, we present a first direct calculation of the Bjorken-x dependence of the PDFs using Large-Momentum Effective Theory (LaMET). An exploratory study of the antiquark/sea flavor asymmetry of these distributions will be discussed. This breakthrough opens an exciting new frontier calculating more complicated quantities, such as gluon structure and transverse-momentum dependence, which will complement existing theoretical programs for the upcoming Electron-Ion Collider (EIC) or Large Hadron-Electron Collider (LHeC).

Speaker: Prof. Huey-Wen Lin (Michigan State University)

Slides Lattice_2016.v2s.pdf

12:30 PM Lunch Break

Women in Lattice

Convener: Ms Vera Guelpers (University of Southampton)

Hadron Spectroscopy and Interactions

Convener: Jozef Dudek (Jefferson Lab)

84 The Rho Resonance from Twisted Mass Lattice QCD

We present new results for $I=1 \ \pi\pi$ scattering with twisted mass fermions utilizing the sLapH method. The breaking of rotational symmetry on the lattice is fully taken into account at multiple moving frames. Our previous calculation is extended by more single and multi-hadron operators and by utilising more irreducible representations.

Speaker: Markus Werner (University of Bonn)

Slides werner_1400.pdf

85 Two-flavor simulations of the rho(770) and the role of the KKbar channel

The $\rho (770)$ meson is the most extensively studied resonance in lattice QCD simulations in two ($N_f=2$) and three ($N_f=2+1$) flavors. We analyze all available phase shifts from $N_f=2$ simulations using unitarized Chiral Perturbation Theory, allowing not only for the extrapolation in mass but also in flavor, $N_f=2\rightarrow N_f=3$. The flavor extrapolation requires information from a global fit to $\pi\pi$ and $\pi K$ phase shifts from experiment. The $K\bar K$ channel has a significant effect and leads to $\rho(770)$ masses surprisingly close to the experimental one. Chiral extrapolations of $N_f=2+1$ simulations are also presented.

Speaker: Mr Bin Hu (Department of Physics, The George Washington University)

Slides Presentation_final.pdf

86 Utilising optimised operators and distillation to extract scattering phase shifts

Distillation is a method of smearing that allows for the efficient computation of correlation functions on the lattice. It vastly reduces the number of operations needed to calculate correlation functions with large bases of operators and all-to-all propagators. In this investigation, we provide a comprehensive comparison of the quality of extracted energy spectra with different amounts of distillation smearing for the isospin-1 $\pi\pi$, $\rho$ like channel. Results are demonstrated in the determination of the mass spectra and also the scattering phase shift and mass and width of the resonant $\rho$ via the Luscher method.

Speaker: Mr Antoni Woss (University of Cambridge)

Slides lattice_2016_woss.pptx

87 Angular and chiral content of the $\rho$ and $\rho^\prime$ mesons

We identify the chiral and angular momentum content of the leading quark-antiquark Fock component for the $\rho(770)$ and $\rho(1450)$ mesons using a two-flavor lattice simulation with dynamical Overlap Dirac fermions. We extract this information from the overlap factors of two interpolating fields with different chiral structure and from the unitary transformation between chiral and angular momentum basis. For the chiral content of the mesons we find that the $\rho(770)$ slightly favors the $(1,0)\oplus(0,1)$ chiral representation and the $\rho(1450)$ slightly favors the $(1/2,1/2)_b$ chiral representation. In the angular momentum basis the $\rho(770)$ is then a $^3S_1$ state, in accordance with the quark model. The $\rho(1450)$ is a $^3D_1$ state, showing that the quark model wrongly assumes the $\rho(1450)$ to be a radial excitation of the $\rho(770)$.

Speaker: Christian Rohrhofer (University of Graz)

Slides rohrhofer.pdf

88 Hadron scattering and resonances

In this talk, I present recent progress towards the determination of resonant systems via lattice QCD. The truncation of the volume -- necessary for lattice QCD calculations -- significantly alters the analytic structure of the theory. For scattering processes involving two-hadron states, this can be circumvented by utilizing formalism to map finite-volume quantities obtained onto the desired infinite-volume observables. I illustrate the power of these techniques by highlighting some important examples in the light sector of QCD.

Speaker: Dr Raul Briceno (Thomas Jefferson National Accelerator Facillity)

Slides lattice_2016.pdf

89 Progress on three-particle quantization condition

We report progress on extending the relativistic model-independent quantization condition for three particles to a broader class of theories, and in checking the formalism. Topics that will be touched on are: (i) the extension to include the possibility of 2->3 and 3->2 transitions and (ii) checks of the formalism by comparing to threshold expansions and to the energy shift of a three-particle Efimov-like bound state.

Speaker: Prof. Stephen Sharpe (University of Washington)

Slides sharpe_lat16.pdf

Hadron Structure

Convener: Dr Zohreh Davoudi (MIT)

90 Disconnected and light connected HVP contributions to the muon anomalous magnetic moment

I present our recent results for the disconnected HVP contribution and report the current status of our light connected HVP contribution to the muon anomalous magnetic moment.

Speaker: Christoph Lehner (BNL)

Slides lattice.v1.pdf

91 The connected and leading disconnected diagrams of the hadronic light-by-light contribution to muon $g-2$

We report our recent lattice calculation of hadronic light-by-light contribution to muon $g-2$ using our recent developed moment method. The connected diagrams and the leading disconnected diagrams are included. The calculation is performed on a $48^3 \times 96$ lattice with physical pion mass and 5.5 fm box size. We expect sizable finite volume and finite lattice spacing corrections to the results of these calculations which will be estimated in calculations to be carried out over the next 1-2 years.

Speaker: Mr Luchang Jin (Columbia University)

Slides lattice2016.pdf

92 The leading order hadronic contribution of the anomalous magnetic moment of the muon with O$(a)$-improved Wilson fermions with Pade approximants from fits and time moments

We present results of our lattice QCD study of the hadronic vacuum polarization (HVP) function with O$(a)$-improved $N_{\rm f}=2$ Wilson fermions with twisted boundary conditions. We discuss the extraction of the leading order hadronic contribution to the anomalous magnetic moment of the muon $\left(a_\mu^{\mathrm{HLO}}\right)$ via the hybrid method involving two steps: (i) To describe the low $Q^2$ range, we construct Pade approximants obtained either from correlated fits to the HVP or from time moments, which we obtain from derivatives of the current-current correlator.(ii) For the large $Q^2$ range we use a numerical integration. We estimate systematic uncertainties of the continuum and chiral extrapolations with the extended frequentist method. Preliminary results for $u,d,s$ and $c$ valence quarks at the physical point for $a_\mu^{\mathrm{HLO}}$ will be presented.

Speaker: Hanno Horch (University of Mainz)

Slides g-2_HannoHorch_Lat2016.pdf

93 Isospin-breaking effects for meson masses and HVP, from Lattice QCD + quenched QED

Lattice calculations of the leading-order hadronic contribution to the muon g-2, from the hadronic vacuum polarisation, are approaching sub-percent level precision. At this level, it becomes important to consider corrections from isospin-breaking. Here, we include quenched QED in our simulations by stochastically generating U(1) gauge configurations and combining these with existing SU(3) gauge configurations. We will present some first results for meson masses and HVP using this method, obtained on a 24^3 x 64, N_f=2+1 ensemble using domain wall fermions. This calculation will be directly compared to the perturbative approach presented by Vera Gülpers.

Speaker: Mr James Harrison (University of Southampton)

Slides presentation4.pdf

94 Leading electromagnetic corrections to meson masses and the HVP

We present a strategy to calculate the leading order electromagnetic corrections to meson masses and the hadronic vacuum polarization. These corrections are computed directly through a QED perturbative expansion of the QCD+QED correlation functions. We will show some first results obtained using $N_f=2+1$ Domain Wall fermions. This calculation will be directly compared to the stochastic approach presented by James Harrison.

Speaker: Ms Vera Guelpers (University of Southampton)

Slides guelpers_lat16.pdf

95 Position-space approach to hadronic light-by-light scattering in the muon $g-2$ on the lattice

The anomalous magnetic moment of the muon currently shows a more than $3\sigma$ discrepancy between the experimental value and recent Standard Model predictions. The theoretical uncertainty is dominated by the hadronic vacuum polarization and the hadronic light-by-light (HLbL) scattering contributions, where the latter has so far only been fully evaluated using different models. To pave the way for a lattice calculation of HLbL, we present an expression for the HLbL contribution to $g-2$ that involves a multidimensional integral over a position-space QED kernel function in the continuum and a lattice QCD four-point correlator. We describe our semi-analytic calculation of the kernel and test the approach by evaluating the $\pi^0$-pole contribution in the continuum.

Speaker: Mr Nils Asmussen (Institut für Kernphysik, Johannes Gutenberg-Universität Mainz)

Slides Nils_Asmussen-Lattice2016.pdf

Nonzero Temperature and Density

Convener: Dr Christian Schmidt (Universitaet Bielefeld)

96 Results on the heavy-dense QCD phase diagram using complex Langevin

Complex Langevin simulations have been able to successfully reproduce results from Monte Carlo methods in the region where the sign problem is mild and make predictions when it is exponentially hard. We present here our study of the QCD phase diagram in the limit of heavy and dense quarks (HDQCD) for 3 different lattice volumes and the boundary between the hadronic phase and the quark-gluon plasma. We also briefly discuss instabilities encountered in our simulations.

Speaker: Mr Felipe Attanasio (Swansea University)

Slides Attanasio.pdf

97 Testing dynamic stabilization in complex Langevin simulations

Complex Langevin methods have been successfully applied in theories that suffer from a sign problem such as HDQCD. We present and illustrate a novel method that ensures that Complex Langevin simulations stay close to the SU(3) manifold, which lead to correct and improved results in the framework of HDQCD and pure gauge simulations. Applying the same technique in fully dynamical QCD simulations shows great potential to allow the determination of the phase diagram from first principles.

Speaker: Dr Benjamin Jaeger (Swansea University)

Slides Jaeger_Lat16.pdf

98 Sign problem in heavy-dense QCD from a density-of-states perspective

We investigate QCD at finite densities of heavy quarks from a density-of-state perspective. Using the LLR approach, we can compute the phase-factor expectation value in the strong sign problem regime with unprecedented precision due to its inherent exponential error suppression. We use our findings to draw conclusions on the approach using phase cumulants.

Speaker: Dr Nicolas Garron (PU)

Slides garron_dos_Lat16.pdf

99 Functional Fit Approach (FFA) for Density of States method: SU(3) spin system and SU(3) gauge theory with static quarks

We study new developments for the Density of States (DoS) method to simulate systems affected by the complex action problem. In particular we use the functional fit approach (FFA). It consists of a restricted Monte Carlo simulation with an additional Boltzmann factor, which allows one to explore the DoS for a given part of the spectrum. We fit the simulation data with a known function to obtain the parameters of the DoS. We apply the approach to two model systems: 1) The SU(3) spin system with a chemical potential; 2) The SU3 gauge theory with static quarks. We discuss the technical challenges and the potential of FFA DoS.

Speaker: Mr Mario Giuliani (University of Graz)

Slides Presentazione_Southampton.pdf

100 Complex Langevin Dynamics for a Random Matrix Model of QCD at finite density

We study a Random Matrix Model for QCD at finite density via Complex Langevin dynamics. This model has a phase transition to a phase with non-zero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables: the baryon density and the chiral condensate. As expected, for simulations close to the chiral limit, the algorithm has wrong convergence properties when the quark mass is in the spectral domain of the quenched Dirac operator. Possible solutions of this problem are discussed.

Speaker: Dr Savvas Zafeiropoulos (Goethe University Frankfurt)

Slides Zafeiropoulos_Lat16.pdf

101 Spontaneous symmetry breaking induced by complex fermion determinant --- yet another success of the complex Langevin method

In many interesting systems, the fermion determinant becomes complex and its phase plays a crucial role in the determination of the vacuum. For instance, in finite density QCD at low temperature and high density, exotic fermion condensates are conjectured to form due to such effects. When one applies the complex Langevin method to such a complex action system naively, one cannot obtain the correct results because of the singular-drift problem associated with the appearance of small eigenvalues of the Dirac operator. Here we propose to add a fermion bilinear term to the action to avoid this problem and extrapolate its coefficient to zero. We test this idea in an SO(4)-invariant matrix model with a Gaussian action and a complex fermion determinant, whose phase is expected to induce the spontaneous breaking of the SO(4) symmetry. Our results agree well with the previous results obtained by the Gaussian expansion method.

Speaker: Dr Yuta Ito (KEK)

Slides Lattice2016.v6.pdf

Physics Beyond the Standard Model

Convener: Prof. Luigi Del Debbio (Edinburgh)

102 Running coupling of twelve flavors

Numerical results are reported on the discrete $\beta$-function of $SU(3)$ gauge theory with $N_f=12$ fundamental fermions in the gradient flow scheme. Controlled continuum extrapolation is performed for $s=2\;$ scale change with $c = \sqrt{8t} / L = 0.2$ targeting 3 tuned values of the renormalized coupling, approximately $g^2=6.0,\; 6.2\;$ and $\;6.4$. Contrary to a previous claim, no evidence is found for a zero of the continuum $\beta$-function.

Speaker: Daniel Nogradi (Eotvos University)

Slides nf12.pdf

103 Light Isosinglet Scalar in Eight Flavor QCD

The LSD Collaboration has recently completed a study of the light hadron spectrum in SU(3) gauge theory with eight light, degenerate flavors. We have observed that the lightest isosinglet scalar meson, also called the sigma, remains essentially degenerate with the pions even when the (pi,sigma) multiplet mass scale falls below half the rho meson mass as a function of the input quark mass. This is clearly quite different from QCD with two light flavors. However, we also observe behavior consistent with the vector meson dominance (VMD) hypothesis, which is quite similar to QCD with two light flavors. Finally, we discuss how the presence of a light sigma in the spectrum affects the standard methodology of lattice gauge theory calculations.

Speaker: Dr George Fleming (Yale University)

Slides GFleming.pdf

104 Studying the Low Energy Effective Theory of Eight Flavor QCD

In recent years, lattice studies of multi-flavor gauge theories near and inside the conformal window have provided strong evidence for the existence of light 0++ states in their spectra, which has led to a renewed interest in strong dynamics as a solution to the Higgs hierarchy problem. An additional requirement to realize a UV complete composite Higgs sector is that observables of low energy scattering be in close agreement with the linear sigma model. We will compute the momentum dependence of the scalar form factor of the pion and of the scattering phase shift of I=2 pi-pi scattering. These quantities will be compared to the linear sigma model and other low energy effective theories. We will also study the vector form factor to test the ansatz of vector meson dominance and to compare to I=1 scattering in a future study. This talk reports on the current progress.

Speaker: Mr Andrew Gasbarro (Yale University)

Slides 8fEFT_final.pdf

105 Flavor singlet mesons in QCD with varying number of flavors

Flavor singlet pseudoscalar and scalar mesons are importat objects for both SM-QCD and technicolor models. The study utilizes the handle of the number of flavors in the many-flavor QCD simulations, which has been performed by LatKMI collaboration. Through this, implications to both SM-QCD and technicolor, which could help understand the dynamics of flavor singlet sector, are anticipated. We report on the on-going study towatds this direction with high-statitics HISQ configurations mainly with $N_f=8$ and $4$.

Speaker: Dr Yasumichi Aoki (KEK)

Slides slide_yaoki_Lattice2016.pdf

106 Discrete $\beta$-function of the SU(3) gauge theory with 10 massless domain-wall fermions

I present the updated results of the discrete $\beta$-function of the $SU(3)$ gauge theory with $N_f=10$ massless optimal domain-wall fermions in the fundamental representation. The renormalized coupling is obtained by the finite-volume gradient flow scheme on $ L^4 $ lattices, for seven lattice sizes: $ L/a = 8, 10, 12, 16, 20, 24, 32 $; and each with $11 - 17$ different lattice spacings parametrized by $ 6/g_0^2 $. The discrete $\beta$-function is extrapolated to the continuum limit using four lattice pairs $(L, 2L)/a =(8, 16), (10, 20), (12, 24)$ and $(16,32)$. This provides stronger evidence of the infrared fixed point at $ g_c^2 \simeq 7 $, which was first reported in arXiv:1603.08854, based on the continuum extrapolation of the discrete $\beta$-function obtained with three lattice pairs.

Speaker: Prof. Ting-Wai Chiu (National Taiwan University)

107 Selected new results from the spectroscopy of the sextet BSM model

We will present results on important spectroscopy problems of the sextet composite Higgs model selected from the light scalar spectrum, vector resonances, the eta’ particle of the axial anomaly, and spectroscopy analysis using a mixed action with restored chiral symmetry of valence fermions.

Speaker: Mr chik him Wong (University of Wuppertal)

Slides presentation.pdf

Standard Model Parameters and Renormalization

Convener: Dr Eliana Lambrou (University of Wuppertal)

108 Quark masses and strong coupling constant with Highly-Improved Staggered Quarks

We present new results on the charm and bottom quark masses as well as the strong coupling constant in 2+1-flavor QCD using Highly Improved Staggered Quark action and gauge configurations generated by HotQCD Collaboration. Our approach is based on calculating the moments of meson correlators and we use a wide range of lattice spacing up to $a^{-1} \sim 4.9$ GeV in our study. The ratios of quark masses $m_c/m_s$ and $m_b/m_c$ are obtained from the combinations of the pseudo-scalar and vector meson masses and found to be $m_c/m_s=11.871(96)$ and $m_b/m_c=4.528(57)$ in the continuum limit. The lattice results of the hyper-fine splitting of the charmonium can reproduce the experimental value in the continuum. We also perform the determination of the strong coupling constant in the $\overline{\rm MS}$ scheme from the moments of pseudo-scalar charmonium correlators and find $\alpha_s(\mu=m_c)=0.3697(56)$, which is the determination of $\alpha_s$ at lowest energy scale so far. For the charm quark mass we obtain $m_c(\mu=m_c)=1.2668(10)$ GeV.

Speaker: Dr Yu Maezawa (YITP, Kyoto University)

Slides Lattice2016_maezawa.pdf

109 Step scaling in X-space: running of the quark mass

We perform a benchmark study of the step scaling procedure for the ratios of renormalization constants extracted from position space correlation functions. We work in the quenched approximation and consider the pseudoscalar, scalar, vector and axial vector bilinears. The pseudoscalar/scalar cases allow us to obtain the non-perturbative running of the quark mass over a wide range of energy scales - from around 15 GeV to nearly 1 GeV - which agrees well with the 4-loop prediction of continuum perturbation theory. We find that step scaling is feasible in X-space and we discuss its advantages and potential problems.

Speaker: Dr Krzysztof Cichy (Goethe-University Frankfurt am Main)

Slides cichy-LAT16.pdf

110 Non-perturbative running of quark masses in three-flavour QCD

We present our results for the computation of the non-perturbative running of renormalized quark masses in $N_f=3$ QCD, between the electroweak and hadronic scales, using standard finite-size scaling techniques. The computation is carried out to very high precision, using massless $\mathcal{O}$(a) improved Wilson quarks. Following the strategy adopted by the ALPHA Collaboration for the running coupling, different schemes are used above and below a scale $\mu_{\rm swi} \sim m_b$, which differ by using either the Schrödinger Functional or Gradient Flow renormalized coupling. We discuss our results for the running in both regions, and the procedure to match the two schemes.

Speaker: Mr David Preti (Instituto de Física Teórica CSIC/UAM)

Slides LATTICE2016_fin.pdf

111 Determination of charm quark mass from temporal moments of charmonium correlator with Mobius domain-wall fermion

We extract the charm quark mass and the strong coupling constant by using the charmonium current correlators with $n_f$ = 2 + 1 Mobius domain wall fermions. The temporal moments of the correlators are sensitive to short-distance physics, and could be also calculated in the continuum theory by perturbative expansion, which is known up to four- loop order.We match our lattice calculation with perturbative result, and extract the charm quark mass with the uncertainty less than 1%. We also confirm the correlators in the vector channel to be consistent with experimental data for R-ratio. We used the ensembles by the JLQCD collaboration at lattice spacings a = 0.083 fm, 0.055 fm and 0.044 fm, are extrapolated to the continuum limit.

Speaker: Katsumasa Nakayama (Nagoya University)

Slides to_LATTICE_2016.pdf

112 Up and down quark masses and corrections to Dashen's theorem from lattice QCD and quenched QED

We present a determination of the corrections to Dashen's theorem and of the individual up and down quark masses from a lattice calculation based on quenched QED and $N_f=2+1$ QCD simulations with 5 lattice spacings down to $0.054 \, \mbox{fm}$. The simulations feature lattice sizes up to $6 \, \mbox{fm}$ and average up-down quark masses all the way down to their physical value. For the parameter which quantifies violations to Dashens's theorem we obtain $\epsilon=0.73(2)(5)(17)$, where the first error is statistical, the second is systematic, and the third is an estimate of the QED quenching error. For the light quark masses we obtain, $m_u=2.27(6)(5)(4) \ \mbox{MeV}$ and $m_d=4.67(6)(5)(4) \, \mbox{MeV}$ in the $\bar{MS}$ scheme at $2 \, \mbox{GeV}$ and the isospin breaking ratios $m_u/m_d=0.485(11)(8)(14)$, $R=38.2(1.1)(0.8)(1.4)$ and $Q=23.4(0.4)(0.3)(0.4)$. Our results exclude the $m_u=0$ solution to the strong CP problem by more than 24 standard deviations.

Speaker: Mr Lukas Varnhorst (University of Wuppertal)

Slides talk_varnhorst.pdf

113 Non-equilibration of topological charge and its effects

[MILC collaboration} In QCD simulations at small lattice spacings the topological charge $Q$ evolves very slowly, and if this quantity is not properly equilibrated it could lead to incorrect results for physical quantities, or incorrect estimates of their errors. We use the known relation between the dependence of masses and decay constants on the QCD vacuum angle $\theta$ and the squared topological charge $Q^2$ together with chiral perturbation theory results for the dependence of masses and decay constants on $\theta$ to estimate the size of these effects and suggest strategies for dealing with them. For the partially quenched case, we sketch an alternative derivation of the known $\chi$PT results of Aoki and Fukaya, using the nonperturbative correct chiral theory worked out by Golterman, Sharpe and Singleton. With the MILC collaboration's ensembles of lattices with four flavors of HISQ dynamical quarks, we measure the $Q^2$ dependence of masses and decay constants and compare to the $\chi$PT forms. The observed agreement gives us some confidence that we can reliably estimate the errors from slow topology change, and even correct for its leading effects.

Speaker: Doug Toussaint (University of Arizona)

Slides topology_lat16_v3.pdf

Theoretical Developments

Convener: Dr Wolfgang Bietenholz (UNAM, Mexico)

114 $B\to K^*$ decays in a finite volume

We propose a framework for the extraction of the $B\to K^*$ decay form factors from lattice data, based on the non-relativistic effective field theory in a finite volume. A possible admixture of the $\eta K$ channel is studied, and the multi-channel Lellouch-Luescher formula is reproduced. Further, a procedure is formulated for the extraction of the form-factors at the resonance pole. The definition of the photon virtuality at the resonance pole is discussed. The limit of an infinitely narrow resonance is investigated in detail in the multi-channel case.

Speaker: Dr Akaki Rusetski (HISKP, University of Bonn, Germany)

Slides lattice-2016_1.pdf

115 Retrieving the optical potential from a Lattice simulation.

We propose a method for the direct extraction of the complex hadron-hadron optical potential (or, equivalently, the phase shift and inelasticity in a given channel) on the lattice, which does not require the use of the multi-channel Lüscher formalism, but the knowledge of a tower of energy levels only. The approach works for any multi-particle states and tested explicitly on a set of synthetic data for the $\pi\eta-K\bar K$ system. Further, we show how a sufficiently large number of energy eigenvalues can be obtained utilizing partial twisting.

Speaker: Dr Maxim Mai (George Washington University)

Slides LATTICE-mai2.pdf

116 A variational method for spectral functions

The Generalized Eigenvalue Problem (GEVP) has been intensively used in the past in order to reliably extract energy levels from time-dependent euclidean correlators calculated in Lattice QCD. We propose an alternative formulation of the GEVP in frequency space. Our approach consists in applying the model independent Backus-Gilbert method to a set of euclidean two-point functions with common quantum numbers. A GEVP analysis in frequency space is then applied to a matrix of estimators that allows us, among other things, to obtain particular linear combinations of the initial set of operators that optimally overlap to different local regions in frequency. This approach can be interesting both for vacuum physics as well as for finite temperature problems.

Speaker: Mr Daniel Robaina (Institute for Nuclear Physics Mainz)

Slides presentacion.pdf

117 Applying recursive numerical integration techniques for solving high dimensional integrals

The error scaling for Markov Chain - Monte Carlo techniques (MC-MC) with $N$ samples behaves like $\frac{1}{\sqrt{N}}$. This scaling makes it often very time intensive to reduce the error of calculated observables, in particular for applications in lattice QCD. It is therefore highly desirable to have alternative methods at hand which show an improved error scaling. One candidate for such an alternative integration technique is the method of recursive numerical integration (RNI). The basic idea of this method is to use Gauss quadrature with Legendre polynomials and apply it iteratively to integrate over observable and Boltzmann weight. In this talk we will present the application of such an algorithm to the topological rotor and the anharmonic oscillator and compare the error scaling to MC-MC results. In particular, we demonstrate that the RNI technique shows an error scaling in $N$ that is at least exponential.

Speaker: Ms Julia Volmer (DESY Zeuthen)

Slides RNI_Lattice.pdf

118 O(3) model with Nienhuis action

We study the O(3) sigma model on a D=2 lattice with a Boltzmann weight linearized in $\beta$ on each link. While the spin formulation now suffers from a sign-problem the equivalent loop model remains positive and becomes particularly simple. By studying the transfer matrix and by performing MC simulations in the loop form we study the mass gap coupling in a step scaling analysis. The question addressed is, whether or not such a simplified action still has the right universal continuum limit. If the answer is affirmative this would be helpful in widening the applicability of worm algorithm methods.

Speaker: Prof. Ulli Wolff (HU Berlin)

Slides Wolff.pdf

119 Tensor RG calculations and quantum simulations near criticality

We reformulate the Ising model, the O(2) model with a chemical potential and the Abelian Higgs model on a 1+1 space-time lattice using the Tensor Renormalization Group (TRG) method. The reformulation allows exact blocking and connects smoothly the classical Lagrangian approach to the quantum Hamiltonian approach. We discuss the linearization of the TRG for the Ising model near the critical point. We calculate the entanglement entropy in the superfluid phase of the O(2) model and show that it obeys the Cardy scaling (c/3)*Ln(L). We calculate the Polyakov loop in the Abelian Higgs model and discuss the possibility of a deconfinement transition at finite volume. We propose Bose-Hubbard Hamiltonians with two species implementable on optical lattices as quantum simulators.

Speaker: Prof. Yannick Meurice (University of Iowa)

Slides meuricelattice2016.pdf

4:00 PM Coffee Break

Algorithms and Machines

Convener: Dr Michael Endres (MIT)

120 Monte Carlo simulation of $\phi^4_2$ and $O(N)\,\phi^4_3$ theories

We report lattice simulations of $\phi^4_2$ and $O(N)\,\phi^4$ models, performed by means a Monte Carlo method based on the all-order strong coupling expansion (worm algorithm). The investigation of the non–perturbative features of the $\phi^4$ continuum limit in two dimensions lead us to the result $g/\mu^2 = 11.15 \pm 0.06_{stat} \pm 0.03_{syst}$ for the critical coupling. Furthermore we present a study of the scaling behaviour of worm and loop size in two-dimensional $O(N)$ model (non-linear $\sigma$-model) and three-dimensional $\phi^4\,O(N)$ model.

Speaker: Ms Barbara De Palma (Istituto Nazionale di Fisica Nucleare (INFN) and Università di Pavia)

Slides talk.pdf

121 Monte Carlo methods in continuous time for lattice Hamiltonians

We solve a variety of sign problems for models in lattice field theory using the Hamiltonian formulation, including Yukawa models and simple lattice gauge theories. The solutions emerge naturally in continuous time and use the dual representation for the bosonic fields. These solutions allow us to construct quantum Monte Carlo methods for these problems. The methods could provide an alternative approach to understanding non-perturbative dynamics of some lattice field theories.

Speaker: Ms Emilie Huffman (Duke University)

Slides Lattice2016Talk.pdf

122 Applications of Jarzynski's relation in lattice gauge theories

Jarzynski's equality is a well-known result in statistical mechanics, relating free-energy differences between equilibrium ensembles with fluctuations in the work performed during non-equilibrium transformations from one ensemble to the other. In this talk, an extension of this relation to lattice gauge theory will be presented, along with numerical results for the $Z_2$ gauge model in three dimensions and for the equation of state in SU(2) Yang-Mills theory in four dimensions. Then, further applications will be discussed, in particular for the Schroedinger functional and for the study of QCD in strong magnetic fields.

Speaker: Mr Alessandro Nada (Università di Torino & INFN, Torino)

Slides lattice16.pdf

123 Computing the density of states with the global Hybrid Monte Carlo

The LLR algorithm is a recent proposal for computing the density of states in lattice gauge theory. This algorithm has been tested in several bosonic models at zero and finite chemical potential with impressive results. Its original formulation is based on the simulation of the theory on restricted action intervals using local Monte Carlo updates.I will discuss a new version of the method based on the global Hybrid Monte Carlo algorithm which is suitable for theories with dynamical fermions. I will present our preliminary result for the study of the SU(2) gauge theory.

Speaker: Dr Roberto Pellegrini (The University of Edinburgh)

Slides density.pdf

124 Overcoming strong metastabilities with the LLR method

It has been shown that the recently proposed LLR method is very efficient at overcoming strong metastabilities that arise near first-order phase transition points. Here we present a systematic study of the performance of the algorithm near (pseudo)critical points on q-state Potts models for q as large as 20, in two and three dimensions. In particular, we shall focus our study on the ergodicity of the replica exchange step and the underlying physical mechanism. Our results for thermodynamic observables (including interface tensions at criticality) are also discussed.

Speaker: Prof. Biagio Lucini (Swansea University)

Slides lucini_lat16.pdf

125 Metadynamics Remedies for Topological Freezing

Metadynamics is a class of powerful algorithms in which the time evolution of a system is modified introducing a history-dependent potential associated with the past values of observables of choice. This has the effect of driving the system away from previously occupied states, ultimately speeding up the evolution of the system. These methods are widely used in biochemistry and computational physics, and are especially suitable for solving problems in which the free energy presents a many-minima landscape. In this talk I will show a successful application of Metadynamics to the critical slowing down of the topological charge in CP(N-1) models, discussing the scaling of the performances with volume and lattice spacing, limitations and future improvements, and giving also a first glance of applications to lattice QCD.

Speaker: Mr Francesco Sanfilippo (University of Southampton)

Slides meta.pdf movie.mp4

Hadron Spectroscopy and Interactions

Convener: Prof. Stephen Sharpe (University of Washington)

126 Kaon Kaon scattering at maximal isospin from $N_f=2+1+1$ twisted mass lattice QCD

We present results for the interaction of two Kaons at maximal isospin. The calculation is based on 2+1+1 flavour gauge configurations generated by the ETM Collaboration featuring pion masses ranging from about 230 MeV to 450 MeV at three values of the lattice spacing. The elastic scattering length $a_0$ is calculated at several values of the bare strange quark and light quark masses. Chiral extrapolations to the physical point are presented and compared to other lattice results.

Speaker: Mr Christopher Helmes (HISKP Universität Bonn)

Slides kk_scat_lat16.pdf

127 An $a_0$ resonance in strongly coupled $\pi \eta$, $K \overline{K}$ scattering from lattice QCD

We present the first calculation of coupled-channel meson-meson scattering in the isospin $=1$, $G$-parity negative sector, with channels $\pi \eta$, $K\overline{K}$ and $\pi \eta'$, in a first-principles approach to QCD. From the discrete spectrum of eigenstates in three volumes extracted from lattice QCD correlation functions we determine the energy dependence of the $S$-matrix, and find that the $S$-wave features a prominent cusp-like structure in $\pi \eta \to \pi \eta$ close to $K\overline{K}$ threshold coupled with a rapid turn on of amplitudes leading to the $K\overline{K}$ final-state. This behavior is traced to an $a_0(980)$-like resonance, strongly coupled to both $\pi \eta$ and $K\overline{K}$, which is identified with a pole in the complex energy plane, appearing on only a single unphysical Riemann sheet. Consideration of $D$-wave scattering suggests a narrow tensor resonance at higher energy.

Speaker: Jozef Dudek (Jefferson Lab)

Slides Dudek.pdf

128 The isospin-0 pion-pion scattering length from twisted mass lattice QCD

We present results for the $\pi\pi$ isospin-0 scattering length calculated in twisted mass lattice QCD. We use a set of $N_f = 2 + 1 + 1$ ensembles with pion mass varying in the range of 230MeV - 510MeV at three different values of lattice spacing and two $N_f=2$ ensembles with one pion mass at its physical value and one at 250MeV. The quark disconnected diagrams are computed with sufficient precision by using the stochastic Laplacian Heaviside quark smearing method. For the first time we extrapolate our lattice results to the physical pion mass and continuum limit.

Speaker: Dr Liuming Liu (University of Bonn)

Slides talk_lattice2016_v1.pdf

129 Lattice operators for scattering of particles with spin

The operators for simulating the scattering of two hadrons with spin will be presented. Three methods give consistent operators for PN, PV, VN and NN scattering, where P, V and N denote pseudoscalar, vector and nucleon. Explicit expressions for all irreducible representations and few lowest momenta will be shown as an example. Correct transformation properties will be demonstrated.

Speaker: Sasa Prelovsek (University of Ljubljana)

Slides prelovsek_lat16.pdf

130 Glueball spectrum from $N_f=2$ lattice QCD study on anisotropic lattices

The glueball spectrum is investigated through a $N_f=2$ lattice QCD study. The gauge configurations are generated with two degenerate flavors of quarks on anisotropic lattices. At two pion masses, say, $m_\pi=580$ MeV and $920$ MeV, we obtain the masses of the scalar, the tensor glueballs, which are in agreement with the results from the previous quenched and unquenched lattice QCD studies. For the pseudoscalar channel, we can get a state of mass roughly 2.4-2.5 GeV by the use of the gluonic lattice operators whose continuum counterparts are $\epsilon_{ijk}B_i^a(D_j B_k)^a$. This state is compatible with the pseudoscalar glueball from the previous quenched lattice QCD studies. We do not observe a clear quark mass dependence of the masses of these states. We also calculate the correlation functions of the topological charge density adopting the gradiant flow smearing scheme. We can seemingly observe a state with a mass around 1 GeV, but fail to obtain a definite result owing to our coarse and small lattices. This state might be the isoscalar $q\bar{q}$ pseudoscalar meson, the $SU(2)$ counterpart of the $SU(3)$ flavor singlet $\eta'$.

Speaker: Prof. Ying Chen (Institute of High Energy Physics, CAS)

Slides Lat_2016_cheny.pdf

Hadron Structure

Convener: Sergey Syritsyn (Jefferson Lab)

131 Hadronic contribution to the muon magnetic moment at the physical point

Recent phenomenological and lattice determinations of the anomalous magnetic moment of the muon $a_\mu$ hint at beyond the Standard Model physics on the 3-4 sigma level. Here we present lattice results for the leading order hadronic contribution of $a_\mu$ obtained from 2+1+1 flavor, staggered quark simulations at the physical point. The various quark flavor contributions, together with their systematics, will be discussed. The results are compared to existing ones in the literature.

Speaker: Dr Taichi Kawanai (Forschungszentrum Jülich (Budapest-Marseille-Wuppertal collaboration))

Slides lattice2016_kawanai.pdf

132 Moments of the hadron vacuum polarization at the physical point

The low, euclidean momentum behavior of the hadron vacuum polarization (HVP) is critical for determining, amongst other quantities, the anomalous magnetic moments of the electron and the muon. Here we present lattice QCD results for the first few moments of the HVP obtained from 2+1+1 flavor, staggered-quark simulations at the physical point. The various quark-flavor contributions, together with their systematics, will be discussed.

Speaker: Dr Kohtaroh Miura (Centre de Physique Theorique, Aix-Marseille Universite, BMW Collaboration)

Slides lattice2016_miura.pdf

133 The strange and charm contributions to $a_\mu$ with physical quark masses using M\"obius domain wall fermions

I present our work on the leading strange and charm quark-connected contributions to the muon anomalous magnetic moment using RBC/UKQCD physical point domain wall fermion ensembles.

Speaker: Mr Spraggs Matthew (University of Southampton)

Slides Talk.pdf

134 Matching issue in quasi parton distribution approach

In recent years, the quasi parton distribution has been introduced to extract the parton distribution functions by the lattice QCD simulation. The quasi and standard distribution share the same collinear IR singularity and the quasi distribution can be factorized into the standard distribution with perturbative matching factor. The quasi parton distribution is known to have power-law UV divergences, which is quite different from the standard distribution. We discuss the UV renormalization scheme in the matching. We also show an example of perturbative matching of the quasi quark distribution between continuum and lattice.

Speaker: Dr Tomomi Ishikawa (RIKEN BNL Research Center)

Slides Lattice16_Ishikawa.pdf

135 Partially conserved axial vector current and applications

A partially conserved axial vector current that satisfies the chiral Ward identity is defined nonperturbatively for improved Wilson fermions. A first application to the nucleon axial vector coupling is presented.

Speaker: Dr Holger Perlt (Institute for Theoretical Physics, University of Leipzig)

Slides Talk_perlt_Lat16_1.pdf

Nonzero Temperature and Density

Convener: Dr Francesco Di Renzo (University of Parma & INFN)

136 Complex Langevin for Lattice QCD at $T=0$ and $\mu \ge 0$.

We simulate Lattice QCD with 2 light quark flavours at zero temperature and finite quark number chemical potential $\mu$. Gauge cooling is applied, along with adaptive rescaling of the updating `time' increment, to stabilize the algorithm. We see evidence for the expected transition at $\mu \approx m_N/3$ and for saturation at large $\mu$. Limitations of the method are discussed.

Speaker: Dr Donald SInclair (Argonne-Seville)

Slides southampton.pdf

137 On complex Langevin dynamics and zeroes of the determinant

In the complex Langevin approach to lattice simulations at nonzero density, zeroes of the fermion determinant lead to a meromorphic drift and hence a need to revisit the theoretical justification. In this talk we discuss how poles in the drift affect the formal justification of the approach and then explore the various possibilities in simple models. The implications of the findings for heavy dense QCD and full QCD are discussed.

Speaker: Prof. Gert Aarts (Swansea University)

Slides talklattice2016.pdf

138 Comparison of CLE and reweighting for QCD at nonzero density

Lattice QCD at non-vanishing chemical potential is studied using the complex Langevin equation (CLE). We compare the results with multi-parameter reweighting both from μ=0 and phase quenched ensembles. A good agreement is found for lattice spacings below ≈0.15 fm. On coarser lattices the complex Langevin approach breaks down. Four flavors of staggered fermions are used on Nt=4,6 and 8 lattices. We also discuss the issue of poles for CLE simulations of HDQCD and full QCD.

Speaker: Dr Denes Sexty (Uni Wuppertal)

Slides sexty_lattice2016.pdf

139 On the condition for correct convergence in the complex Langevin method

The complex Langevin method (CLM) is a promising way to perform the path integral with a complex action based on a stochastic equation for complexified dynamical variables. It is known, however, that the CLM gives wrong results in some cases, while it works, for instance, in finite density QCD in the deconfinement phase or in the heavy dense limit. In this talk, we revisit this issue starting with a finite Langevin step-size. We find that there is a subtlety in taking the zero step-size limit, although the previous argument used a continuous time from the beginning. Also there is a subtlety in using the time-evolved observables, which play a crucial role in the argument. These subtleties require that the probability distribution of the drift term should be suppressed exponentially at large magnitude. We demonstrate our claim in some examples including chiral Random Matrix Theory and show that our criterion is indeed useful in judging whether the results obtained by the CLM are trustable or not.

Speaker: Shinji Shimasaki (Keio University)

Slides lattice2016_v7.pdf

140 Gauge cooling for the singular-drift problem in the complex Langevin method - an application to finite density QCD

The complex Langevin method is a promising approach to complex action systems, which suffer from the sign problem. In particular, the use of gauge cooling enabled the studies of finite density QCD either in the deconfined phase or in the heavy dense limit. In the confined phase with light quarks, however, the method does not work as it is due to the singularities in the fermion drift term caused by small eigenvalues of the Dirac operator with the quark mass. In a previous paper, we proposed that this singular-drift problem can be overcome by the gauge cooling with different criteria for choosing the complexified gauge transformation, and showed that the method works in chiral Random Matrix Theory even at small quark mass. Here, we apply the same idea to QCD at finite density with light quarks and present some preliminary results.

Speaker: Dr Keitaro Nagata (KEK)

Slides Nagata2016_07_Lattice5.pdf

141 Reweighting trajectories from the complex Langevin method

We introduce the reweighted complex Langevin method, which enlarges the applicability range of the complex Langevin method by reweighting the complex trajectories. In this reweighting procedure both the auxiliary and target ensembles have a complex action. We validate the method by applying it to a random matrix model for QCD and to two-dimensional strong-coupling QCD, both at nonzero chemical potential, and observe that it gives access to mass regions that could otherwise not be reached with the complex Langevin method.

Speaker: Dr Jacques Bloch (University of Regensburg)

Slides Bloch_Lattice2016.pdf

Physics Beyond the Standard Model

Convener: Daniel Nogradi (Eotvos University)

142 Numerical Analysis of Discretized ${\mathcal N}=(2,2)$ SYM on Polyhedra

We investigate the two-dimensional $\mathcal{N}=(2,2)$ supersymmetric Yang-Mills (SYM) theory on the discretized curved space both from theoretical and numerical points of view. We first show that the number of the supersymmetry of the continuum $\mathcal{N}=(2,2)$ SYM theory on any curved manifold is enhanced to two by considering an appropriate $U(1)$ gauge backgrounds associated with the $U_{V}(1)$ symmetry. We then show that the generalized Sugino model, which was proposed in our previous work, can be identified to the discretization of the SUSY enhanced theory, where one of the supersymmetries is kept and the other one is restored in the continuum limit. The $U_{A}(1)$ anomaly of the continuum theory is maintained also in the discretized theory as an unbalance of the number of the fermions. We study the discretized supersymmetric model based on the numerical Monte-Carlo simulation. In the process, we propose a novel phase-quenched approximation, which we call the ``anomaly-phase-quench approximation". We find that the Ward-Takahashi (WT) identity expected from the analytical study realizes in the model and there is no sign-problem by adopting the anomaly-phase-quench method. The result is the first numerical observation for the supersymmetric lattice model on the curved space with generic topologies.

Speaker: Dr Syo Kamata (Keio University)

Slides Lattice2016_kamata.pdf

143 S-duality in lattice N=4 super Yang-Mills

Formulations of lattice supersymmetry over the last decade have been able to significantly reduce the amount of fine-tuning necessary in order to obtain the correct continuum limit. In the case of N=4 super Yang-Mills, the approach that has emerged as the best path forward is based on a topological twisting of the theory. Montonen and Olive found evidence that a duality could exist in Yang-Mills with adjoint scalars. In this scheme, the 't Hooft-Polyakov monopole is dual to the W boson,leading to a theory equivalent to the original one, but with magnetic charge replacing electric charge. The duality is believed to be realized in N=4 super-Yang-Mills. We are pursuing numerical, nonperturbative evidence for this S-duality using our lattice formulation. The various tricks that are necessary for doing this will be described.

Speaker: Prof. Joel Giedt (Rensselaer Polytechnic Institute)

Slides lat16_talk.pdf

144 Latest results from lattice N=4 supersymmetric Yang--Mills

I will present results from numerical studies of maximally supersymmetric Yang--Mills theory, focusing on the scaling dimension of the Konishi operator. Working with a lattice formulation that exactly preserves one supersymmetry at non-zero lattice spacing, we employ an improved action developed in 2015 that dramatically reduces lattice artifacts. Using this new improved action we are exploring a range of 't Hooft couplings for two-, three- and four-color gauge theories, to bridge the perturbative regime and the onset of strong-coupling AdS/CFT duality in the large-N limit. Among the various quantities we are investigating the Konishi operator is particularly significant as the simplest conformal operator with a non-trivial anomalous dimension.

Speaker: David Schaich (Syracuse University)

Slides lattice16.pdf

145 Spectroscopy of two dimensional N=2 Super Yang Mills theory

Albeit the standard model is the most successful model of particles physics, it still has some theoretical shortcomings, for instance the hierarchy problem, the absence of dark matter, etc. . Supersymmetric extensions of the standard model could be a possible solution to these problems. One of the building blocks of these supersymmetric models are supersymmetric gauge theories. It is expected that they exhibit interesting features like confinement, chiral symmetry breaking, magnetic monopoles and the like.
We present new results on N=2 Super Yang Mills theory in two dimensions. The lattice action is derived by a dimensional reduction of the N=1 Super Yang Mills theory in four dimensions. By preserving the R symmetry of the four dimensional model we can exploit Ward identities to fine tune our parameters of the model to obtain the chiral and supersymmetric continuum limit. This allows us to calculate the mass spectrum at the physical point and compare these results with effective field theories.

Speaker: Mr Daniel August (Friedrich Schiller University Jena)

Slides lattice2016.pdf

146 D=5 Maximally Supersymmetric Yang-Mills on the Lattice

Maximally supersymmetric Yang-Mills theory in five dimensions has generated a lot of interest in the recent years. It takes part in the gauge-gravity duality and its finite temperature properties have been investigated recently in the planar limit. This theory is also interesting through its conjectured relationship to the six-dimensional (2,0) theory, which is still controversial. In this talk we describe the lattice construction of D=5 maximally supersymmetric Yang-Mills theory. The lattice theory preserves one supercharge exact at finite lattice spacing. This supersymmetric lattice formulation can be used to explore the non-perturbative regime of the continuum target theory. It would be interesting to find a nontrivial UV fixed point from the lattice theory for D=5 theory since the fixed point can provide a UV completion and non-perturbative definition of the theory.

Speaker: Dr Anosh Joseph (University of Cambridge)

Slides JOSEPH_Anosh_LAT16.pdf

147 Simulations of N=1 supersymmetric Yang-Mills theory with three colours

We report on our recent results regarding numerical simulations of the four dimensional, N=1 Supersymmetric Yang-Mills theory with SU(3) gauge symmetry and light dynamical gluinos.

Speaker: Dr pietro giudice (University of Muenster)

Slides lattice2016susysu3_giudice_ver1.pdf

Theoretical Developments

Convener: Prof. Masanori Okawa (Hiroshima University)

148 Six-dimensional regularization of chiral gauge theories on a lattice I

We propose a 6-dimensional lattice regularization of chiral gauge theories. In our formulation, Weyl fermions are localized on the junction of two different domain-walls. One domain-wall naturally exhibits the Stora-Zumino chain of the anomaly descent equations. Another domain-wall mediates a similar inflow of the global anomalies. The anomaly free condition is equivalent to requiring the measure of the 6-dimensional Dirac fermions to cancel the axial U(1) and parity anomalies. ``Localizing'' the gauge fields on the 4-dimensional junction using the Yang-Mills gradient flow, as proposed by Grabowska and Kaplan, we non-perturbatively define the 4-dimensional path integral of the target chiral gauge theory. In the first talk, we present the basic idea of our formulation, emphasizing on why the 6-th dimension is needed for the global anomalies. In the second talk, we explain our lattice set-up in details.

Speaker: Dr Hidenori Fukaya (Osaka University)

Slides Lattice2016Fukaya6DCGTv2.pdf Lattice2016Fukaya6DCGTv2.pptx

149 Six-dimensional regularization of chiral gauge theories on a lattice II

We propose a 6-dimensional lattice regularization of chiral gauge theories. In our formulation, Weyl fermions are localized on the junction of two different domain-walls. One domain-wall naturally exhibits the Stora-Zumino chain of the anomaly descent equations. Another domain-wall mediates a similar inflow of the global anomalies. The anomaly free condition is equivalent to requiring the measure of the 6-dimensional Dirac fermions to cancel the axial U(1) and parity anomalies. ``Localizing'' the gauge fields on the 4-dimensional junction using the Yang-Mills gradient flow, as proposed by Grabowska and Kaplan, we non-perturbatively define the 4-dimensional path integral of the target chiral gauge theory. In the first talk, we present the basic idea of our formulation, emphasizing on why the 6-th dimension is needed for the global anomalies. In the second talk, we explain our lattice set-up in details.

Speaker: Mr Ryo Yamamura (Osaka U.)

Slides Lattice2016Yamamura6DCGT.pptx

150 Borici-Creutz fermions on 2-dim lattice

Minimally doubled fermions(MDF) having only two species could be promising formalism to study chiral fermion on a lattice. The action being ultra-local, one expects that the MDF formulations might provide computationally cheaper alternatives to the existing lattice chiral formulations. Borici-Creutz fermion is one such minimally doubled fermion formulation. In this work, we explore the Borici-Creutz fermion formulation in simple a 2d Gross-Neveu model and in QED2 with Hybrid Monte Carlo simulation. We study chiral symmetry breaking and mass spectrum in Gross-Neveu model .

Speaker: Mr Jishnu Goswami (IIT Kanpur)

Slides test.pdf

151 Sea quark QED effects and twisted mass fermions

We show that maximally twisted mass fermions can be employed to regularize on the lattice the fully unquenched QCD+QED theory with vanishing theta-term. We discuss how the critical mass of the up and down quarks can be conveniently determined beyond the electroquenched approximation by imposing that certain symmetries of continuum QCD+QED, which are broken by Wilson terms, are restored (up to cutoff effects). A mixed action setup is sketched that allows to extend the computation of the leading isospin breaking corrections to physical observables via the RM123 method beyond the electroquenched approximation by using ETMC (pure QCD) gauge configurations with N_f=2+1+1 dynamical quark flavours, with only O(a^2) lattice artifacts.

Speaker: Prof. Roberto Frezzotti (University of Rome Tor Vergata, Physics Department and INFN - Sezione di Roma Tor Vergata)

Slides frezzotti.pdf

152 Search for a continuum limit of the PMS phase

Previous studies of a simple four-fermion model with staggered fermions in 3d have shown the existence of an exotic quantum critical point, where one may be able to define a continuum limit of the Paramagnetic Strong Phase (or the PMS phase). We believe the existence of the critical point suggests a new mechanism for generating fermion masses. In this work we begin the search for this quantum critical point in 4d by extending the 3d model to 4d. Unlike in 3d, now we do find evidence for an intermediate spontaneously broken phase (FM phase) and are able compute the phase boundaries accurately. In terms of the bare coupling, the width of the intermediate region appears to be quite small.

Speaker: Venkitesh Ayyar (Duke University)

Slides Venkitesh_lattice_2016

153 Tensor renormalization group approach to higher dimensional fermions

We apply the higher order tensor renormalization group to two and three dimensional lattice fermion systems. To deal with the tensor network including Grassmann numbers, higher order Grassmann tensor renormalization group (HOGTRG) is introduced. Because of its deterministic property, HOGTRG is perfectly free of the sign problem. We analyze the well-known systems such as the Gross–Neveu model using HOGTRG, and test the validity of the new algorithm.

Speaker: Mr Ryo Sakai (Kanazawa University)

Poster

154 A local update algorithm for supersymmetric Yang-Mills quantum mechanics

We present a local update algorithm for gauge theories with dynamical fermions which allows simulations in fixed canonical sectors. As a first application we perform canonical simulations in N=4 supersymmetric Yang-Mills quantum mechanics without a sign problem. Compared to previous studies, we obtain results with significantly better accuracy. We also discuss some aspects of the physics of this theory, including the appearance of flat directions in the bosonic potential and of phase transitions related to those.

Speaker: Prof. Urs Wenger (AEC University of Bern)

155 Calculation of Quark Condensates and Chirality using Improved Staggered Fermions

We study quark condensates using improved staggered fermions, where zero modes of the Dirac operator give simple poles in the chiral limit. We present a new method to identify the zero modes and to subtract their contribution from the quark condensates. Meanwhile we also identify the quantum numbers of the zero modes in the staggered fermion formalism, using the spectral flow method. All the numerical results are calculated using HYP-smeared staggered fermions on MILC asqtad lattices and on MILC HISQ lattices.

Speaker: Mr Hwancheol Jeong (Seoul National University)

Poster hwancheol_lattice2016.pdf

156 Chiral phase transition in (2 + 1)-flavor QCD on $N_{\tau} = 6$ lattices

We present updated studies of chiral phase transition in $N_{f}=2+1$ QCD. Simulations have been performed with Highly Improved Staggered Quarks (HISQ) on lattices with temporal extent $N_{\tau} = 6$ at vanishing baryon chemical potential. We updated our previous study (1511.00553) by extending the temperature window from (140MeV, 150MeV) to (140MeV, 170MeV). The strange quark mass was chosen to its physical value $m_{s}^{phy}$, and five values of two degenerate light quark masses $(m_{l})$ are varied from $m_{s}^{phy}/80$ to $m_{s}^{phy}/20$ which correspond to a Goldstone pion mass ranging from 80 MeV to 160 MeV in the continuum limit. The universal scaling behaviour of the QCD chiral phase transition is investigated by studying the temperature and quark mass dependence of chiral condensates and chiral susceptibilities. The window of criticality compared to previous studies is also discussed.

Speaker: Mr Sheng-Tai Li (Central China Normal University)

157 Flux Tubes at Finite Temperature

We show the flux tubes produced by static quark-antiquark, quark-quark and quark-gluon charges at finite temperature. The sources are placed in the lattice with fundamental and adjoint Polyakov loops. We compute the square densities of the chromomagnetic and chromoelectric fields above and below the phase transition. Our results are gauge invariant and produced in pure gauge SU(3). The codes are written in CUDA and the computations are performed with GPUs.

Speaker: Prof. Pedro Bicudo (IST - LISBOA)

Poster Poster_v2.pdf

158 Further Study of BRST-Symmetry Breaking on the Lattice

We evaluate the so-called Bose-ghost propagator in minimal Landau gauge, for the SU(2) case in four dimensions. We consider lattice volumes up to $120^4$ and physical lattice extents up to 13.5 fm. We investigate discretization effects, as well as the infinite-volume and continuum limits. A nonzero value for this quantity provides direct evidence of BRST-symmetry breaking, related to the restriction of the functional measure to the first Gribov region.

Speaker: Mr Attilio Cucchieri (University of São Paulo)

Poster lattice16bis.pdf

159 Ground state charmed meson and baryon spectra for $N_f=2+1+1$

We present a study of the charmed meson and baryon ground state spectra on the electrically neutral subset of the BMW $N_f=2+1+1$ gauge configurations that utilise the 3-HEX smeared clover action. The analysis focuses on a systematic evaluation of the hyperfine mass splittings of the doubly charmed $J/\psi$ and $\eta_{c}$ mesons and the singly charmed $D_s^*$ and $D_s$ mesons, with the aim to understand the significant cut-off effects that can accompany Wilson type fermion measurements.

Speaker: Thomas Rae (University of Wuppertal)

160 Hierarchically deflated conjugate residua

Hierarchically deflated conjugate residual We present a new class of multigrid solver algorithm suitable for the solution of 5d chiral fermions such as Domain Wall fermions and the Continued Fraction overlap. Unlike HDCG \cite{arXiv:1402.2585}, the algorithm works directly on a nearest neighbour fine operator. The fine operator used is Hermitian indefinite, for example $\Gamma_5 D_{dwf}$, and convergence is achieved with an indefinite matrix solver such as outer iteration based on conjugate residual. As a result coarse space representations of the operator remain nearest neighbour, giving an 8 point stencil rather than the 81 point stencil used in HDCG. It is hoped this may make it viable to recalculate the matrix elements of the little Dirac operator in an HMC evolution.

Speakers: Dr Azusa Yamaguchi (Software Architect), Prof. Peter Boyle (University of Edinburgh)

161 Looking forward to new lattice inputs for flavour phenomenology

We review the current status of HQE predictions for neutral meson mixing and related observables. A comparison with most recent data shows a confirmation of the HQE, but also leaves sizeable space for new physics effects. We also point out what improved lattice inputs might be most useful for unambiguously identifying new physics in mixing observables.

Speaker: Mr Matthew Kirk (IPPP, Durham University)

Poster matthew_kirk_lattice2016_poster.pdf

162 Mass anomalous dimension of SU(2) using the spectral density method

We study the mass anomalous dimension of SU(2) with $N_f=6$ and $N_f = 8$ in both massless and massive quark cases for a range of gauge coupling values. In the massless case we find behaviour consistent with results obtained using the Schrödinger functional method.

Speaker: Mr Joni Suorsa (University of Helsinki, Helsinki Institute of Physics)

Poster POSTERI.pdf

163 Perturbative calculation of $Z_q$ and $Z_m$ at the one-loop level using improved staggered quarks

We present results of matching factors for $Z_q$ and $Z_m$ calculated perturbatively at the one loop level with improved staggered quarks. We calculate $Z_q$ and $Z_m$ with HYP-smeared staggered quarks. Final results of $Z_q$ and $Z_m$ at $\mu = 2 \ \text{GeV}$ and $3 \ \text{GeV}$ in the $\overline{\text{MS}}$ scheme are given in tables.

Speaker: Mr Benjamin Jaedon Choi (Seoul National University / Lattice Gauge Theory Research Center)

164 Platform Independent Profiling of a QCD Code

The supercomputing platforms available for high performance computing based research evolve at a great rate. However, this rapid development of novel technologies requires adaptations and optimizations of the existing codes for each new machine architecture. In such context, minimizing time of efficiently porting the code on a new platform is of crucial importance. A possible solution is to use coarse grain simulations of the application that can assist in detecting performance bottlenecks. We present a procedure of implementing the intermediate profiling for openQCD code that will enable the global reduction of the cost of profiling and optimizing this code commonly used in the lattice QCD community. Our approach is based on well-known SimGrid simulator, which allows for fast and accurate performance predictions of the codes on HPC architectures. Additionally, accurate estimations of the program behavior on some future machines, not yet accessible to us, are anticipated.

Speaker: Dr Marina Krstic Marinkovic (CERN)

Poster lattice16_poster.pdf

165 Pseudo-scalar decay constants on three-flavour CLS ensembles with open boundaries

We determine the masses and the pseudo-scalar decay constants of charmed mesons using non-perturbatively O($a$) improved Wilson quarks. Our analysis is based on the $N_{\rm f}=2+1$ ensembles using open boundary conditions, generated within the CLS effort. The status of results for 2 lattice spacings, $a\approx 0.086$ fm and $a\approx 0.064$ fm, will be presented. The pion mass is varied from 420 to 220 MeV. This is part of a continuing analysis by the RQCD and ALPHA Collaborations, aiming at a stable continuum extrapolation using several lattice spacings. To extrapolate to the physical masses, we follow both, the $(2m_l+m_s)=\mathrm{const.}$ and $m_s=\mathrm{const.}$ line.

Speaker: Mr Stefan Hofmann (Unversity of Regensburg) (German)

166 Relaxation time of the fermions in the magnetic field (II) - away from strong magnetic field limit -

The relaxation time for the fermions in the magnetic field is needed for estimate the chiral magnetic effect. However, it has been estimated only in the strong magnetic field. We discuss the relaxation time away from the strong magnetic field limit.

Speaker: Prof. Tetsuya Onogi (Osaka University)

Poster 214_onogi.pdf

167 RG scaling at chiral phase transition in two-flavor QCD

We investigate the nature of the chiral phase transition using the RG improved gauge action and the Wilson quark action with two degenerate quarks on $32^3\times 16$, $24^3\times 12$, and $16^3\times 8$ lattices. We introduce RG scaling relations for both the time direction and the spacial effective masses of mesons at the chiral phase transition point. Numerical results of effective masses at the chiral phase transition on the three sizes of lattices are excellently on the universal limiting curves for the pseudo-scalar meson and vector meson, respectively, except for three data points at short distance of each lattice. The results imply the effective masses of pion and vector meson vanishes as $1/N$ in the continuum limit with $N \, a=$ constant. The fact that the scaling relations are satisfied and the effective masses becomes zero in the continuum limit strongly implies the transition is of second order. When the quark is massive at the chiral phase transition in the deconfining side, the hyper-scaling is verified with $\gamma^{*}\simeq 0.5.$

Speaker: Prof. Ken-ichi Ishikawa (Hiroshima University)

Slides Lattice2016iwasaki_v2.pdf

168 Simulation of SU(2) gauge theory with improved domain-wall fermions

In this work, we study SU(2) gauge theory with many flavors using the improved domain-wall fermions, which is realized by the stout-HYP link smearing and the optimal domain-wall formulation. In contrast to the standard domain-wall fermions used in the previous studies, it enables us to investigate the small fermion mass region due to the much suppressed residual mass. With the improved domain-wall fermions, the spectrum and the residual mass are examined on previously generated configurations as well as in dynamical simulations. We also discuss the extension to simulations of the epsilon-regime.

Speaker: Dr Hideo Matsufuru (High Energy Accelerator Research Organization (KEK))

Poster lattice2016.pdf

169 Some Statistics on Women in Lattice QCD

We present a sampling of analyses concerning the gender ratio of plenary speakers during the years 2000-2016 and make comparisons with other conferences, such as the APS April meeting. Please stop by to discuss ideas for how to make our field more accessible to women and minorities. We are preparing for an in-depth survey of the lattice field and welcome any ideas or suggestions. To leave post-conference comments and read about news affecting women in our field, see our Facebook page: https://www.facebook.com/WLQCD

Speaker: Prof. Huey-Wen Lin (Michigan State University)

Poster WLQCD Poster

170 Status report on $\varepsilon_K$ with lattice QCD inputs

We present results of the indirect CP violation parameter in the neutral kaon system, $\varepsilon_K$ calculated using lattice QCD inputs including $\hat{B}_K$, $\xi_0$, $V_{us}$, and $V_{cb}$.

Speaker: Prof. Weonjong Lee (Seoul National University)

171 Strange Quark Magnetic Moment and Charge Radius of the Nucleon at Physical Point

We present a lattice QCD calculation of the strange quark contribution to the proton's magnetic moment and the charge radius at the physical pion mass. The finite lattice spacing and finite volume corrections are included in a global fitting on three lattices with different lattice spacings, different volumes, and three sea quark masses. We obtain the strange magnetic moment $G^s_M(0) = - 0.073(17)\, \mu_N$ and strange charge radius $\langle r^2_s\rangle_E = -0.0047(22) \,\text{fm}^2$. Additionally, we present our results of the disconnected $u$, $d$-quarks contribution to the proton's electromagnetic form factors.

Speaker: Raza Sufian (University of Kentucky, United States)

172 The Hadronic Vacuum Polarisation contribution to the anomalous magnetic moment of the muon

We report on the HPQCD calculation of the u/d HVP contribution to a_mu, discussed in arXiv:1601.03071. This allows us to obtain a total HVP contribution from u, d, s and c quarks and including an estimate of disconnected pieces and QED and isospin effects of 666(6)(12) x 10^{-10}. Our result implies a discrepancy between the experimental determination of a_mu and the Standard Model of 3 sigma. We discuss prospects for improvements to this calculation underway with the MILC and Fermilab Lattice Collaborations.

Speaker: Prof. Christine Davies (University of Glasgow)

Poster amu-poster-lat16.pdf

173 Towards extracting the timelike pion form factor on CLS 2-flavour ensembles

Results are presented from an ongoing study of the $\rho$ resonance. We use the LapH-smearing approach in order to create correlator matrices involving $\rho$ and $\pi\pi$ interpolators. The study is done in a centre-of-mass frame and several moving frames. We are able to extract effective-energy levels by solving the GEVP of those correlator matrices. The initial exploratory study is being done on a CLS 2-flavour lattice with a pion mass of $451$ $\mathrm{MeV}$ using $\mathcal{O}(a)$ improved Wilson fermions. One aim of this work is to extract the timelike pion form factor after applying the Lüscher formalism. We also have all the ingredients ready which allow us to integrate this study with the existing Mainz programme for the calculation of the hadronic vacuum polarization contribution to the muon $g-2$. We plan to extend our study to lower pion masses and larger lattices in the future, including ensembles with $2+1$ flavours.

Speaker: Mr Felix Erben (University Mainz)

Poster poster.pdf

174 Tuning of hopping parameters in Oktay-Kronfeld action for heavy quarks on the $N_f=2+1+1$ MILC HISQ ensemble.

We determine hopping parameters of the Oktay-Kronfeld (OK) action for charm and bottom quarks. We use $N_f=2+1+1$ MILC HISQ ensembles (with $a\approx0.12$fm, $am_l=0.0102$, $am_s=0.0509$ and $am_c=0.635$). As a key ingredient, we compute the masses of pseudoscalar and vector mesons $B_s^{\ast}$, $D_s^{\ast}$ and their hyperfine splittings; the valence light quark is simulated with HISQ action. We also monitor the inconsistency parameters to confirm the improvement.

Speaker: Mr Sungwoo Park (Seoul National University)

Poster poster_sungwoo_park.pdf

175 Update on Nf=3 finite temperature QCD phase structure with Wilson-Clover fermions

We will present an update on analysis of the phase structure for finite temperature QCD with 3-flavor non-perturbatively O(a) improved Wilson-Clover fermions and Iwasaki gauge action. In our previous study, it was shown that the value of kurtosis of quark condensate at the critical point tends to deviate from that of 3D Z_2 universality class when increasing the temporal lattice sizes N_T=8 and 10, while the values at smaller N_T=4 and 6 are consistent with that of Z_2 . We will discuss possible sources of this phenomenon and present results of new analysis.

Speaker: Dr Shinji Takeda (Kanazawa University)

Poster takeda20160726_A0.pdf

176 Zero-momentum SU(2) gluon correlator at various boundary conditions

We make simulations of the zero-momentum $SU(2)$ Landau gauge gluon correlator both for periodic and zero-field boundary conditions at varying $\beta$ and $L_t * L_s^3$ lattice sizes.

Speaker: Dr Igor Bogolubsky (Joint Institute for Nuclear Research)

177 A G(2)-QCD Neutron Star

G2-QCD, i.e. QCD with the gauge group SU(3) replaced by the exceptional group G(2), shares many features with SU(3). But it is accessible at finite density on the lattice, as it has no sign problem, and at the same time has a neutron. Therefore, this theory can sustain in princple neutron star. Using the equation of state for this theory from lattice simulations, we solve the Oppenheimer-Volkoff equation and obtain the mass-radius-relation of such neutron stars. This study shows how different phases, visible in the equation of state, influence the mass-radius relation, and therefore gives guidance for the case of full QCD and true neutron stars.

Speaker: Ms Ouraman Hajizadeh (University of Graz)

178 Applications of Gradient flow to Non-perturbative renormalization of quark bi-linears

Results of a non-perturbative determination of RI-MOM renormalization constants for smeared quark bi-linear operators are presented. These operators are smeared using the gradient flow, enabling the smearing scale to be fixed in physical units. As a result, smeared matrix elements are free of power divergences in the lattice spacing, which allows easier control of the continuum limit of these matrix elements. Potential applications to calculations of twist-2 matrix elements are discussed.

Speaker: Prof. Kostas Orginos (College of William and Mary/JLAB)

179 Approaching the conformal window in SU(2) field theory: a systematic study of the spectrum for Nf=2,4,6, and 8.

It is expected that SU(2) gauge theory with Nf fundamental fermions has an infrared fixed point when Nf is between ∼ 6 and 10. We study the hadron spectrum and scale setting in SU(2) gauge field theory with Nf = 2,4,6,8 using hypercubic stout smeared Wilson-clover (HEX) action. The case Nf = 2 is QCD-like, Nf = 6 is close to the lower edge of the conformal window, and Nf=8 is inside the conformal window. We study the hadron spectrum and decay constants of these theories, and use the gradient flow approach to determine the length scales.

Speaker: Sara Tähtinen (University of Helsinki, Helsinki Institute of Physics)

Poster ST_poster.pdf

180 BSM Kaon mixing at the Physical Point

I present preliminary results for Kaon Mixing Beyond the Standard Model at the physical point.

Speaker: Ms Julia Kettle (University of Edinburgh)

181 Charmed meson physics from three-flavour lattice QCD

We report on analysis aspects within a joint ongoing effort of the ALPHA and RQCD Collaborations to compute charmed meson masses and the leptonic decay constants $f_{{\rm D}}$ and $f_{{\rm D}_{\rm s}}$ in $(2+1)$-flavour lattice QCD, employing non-perturbatively O($a$) improved Wilson quarks and the tree-level Symanzik-improved gauge action. Our studies make use of large-volume CLS configurations at two lattice spacings ($a\approx 0.086,0.064$ fm) with open boundary conditions. In particular, we present our implementation of distance preconditioning (as proposed by de Divitiis et al.) for the calculation of heavy quark propagators and discuss the resulting accuracy improvements of charmed meson correlators and its impact on the extraction of charmed meson masses and decay constants.

Speaker: Mr Kevin Eckert (WWU Muenster)

Poster poster_Kevin_Eckert.pdf

182 Complex Langevin Dynamics In 1+1d QCD At Non-Zero Densities

We present our results obtained from gauge cooled complex Langevin simulations in 1+1D QCD at non-zero densities in the strong coupling regime with unrooted staggered fermions. For small quark masses there are regions of the chemical potential where this method fails to reproduce correct results. In theses parameter ranges we studied the effect of different gauge cooling schemes on the distributions of the fermion determinant as well as of observables.

Speaker: Mr Sebastian Schmalzbauer (Goethe-Universität Frankfurt, Universität Regensburg)

Poster lattice2016_poster.pdf

183 Discussion of the Loop Formula for the fermionic determinant

A formula expressing the fermionic determinant as an infinite product of smaller determinants is here derived and discussed. These smaller determinants are of a fixed size, independent of the size of the lattice and are indexed by loops of increasing length. The application of the formula requires convergence considerations.

Speaker: Dr Ion-Olimpiu Stamatescu (I.T.P., University Heidelberg)

Poster poster_L16.pdf

184 Fermions with long-range interactions using a matrix-product-states approach

The long-range t-V model of fermions on a lattice is known to exhibit a transition between a Luttinger liquid phase and a Mott insulator phase [1]. At insulating densities, one can tailor the potential energy of the model in such a way that one forces a quantum phase transition to either another insulating charge-density-wave phase, a bond-order phase or a Luttinger liquid [2]. We show how to construct a matrix product operator representation of the Hamiltonian of the t-V model and we present phase diagrams calculated using the matrix-product-states approach [3]. We compare these phase diagrams with results obtained in the atomic limit. References ---------- 1. G. Gómez-Santos, Phys. Rev. Lett. 70, 3780 (1993). 2. P. Schmitteckert and R. Werner, Phys. Rev. B 69, 195115 (2004); T. Mishra et al., Phys. Rev. B 84, 115135 (2011). 3. D. Perez-Garcia et al., Quantum Inf. Comput. 7, 401 (2007); F. Verstraete et al., Adv. Phys. 57, 143 (2008).

Speaker: Mr Marcin Szyniszewski (Lancaster University)

Poster Marcin_Szyniszewski_-_Fermions_with_long_range_interactions.pdf

185 Gradient flow observables and boundary O(a) improvement of the Schroedinger functional

The gradient flow provides a new class of renormalized observables which can be measured with high precision in lattice simulations. In principle this allows to improve lattice actions a la Symanzik by requiring such observables to take their continuum values already at finite lattice spacing. At lowest order of perturbation theory we here try to identify such improvement conditions for the O(a) counterterm at the Schroedinger functional boundaries. We study the action density, E(t,x), separately for colour electric and magnetic components and with different discretizations of the observable and the flow.

Speaker: Ms Argia Rubeo (TCD (Trinity College Dublin))

Slides conference_poster_3.pdf

186 Heavy-heavy current improvement for calculation of $\bar{B}\rightarrow D^{(*)}\ell \bar{\nu}$ semi-leptonic form factors using the Oktay-Kronfeld action -- 2

The Oktay-Kronfeld action is a highly improved version of the Fermilab action and systematically reduces heavy quark discretization effects through $\mathcal{O}(\lambda^3)$ in HQET power counting, for the heavy-light meson spectrum. To calculate $\bar{B}\rightarrow D^{(*)}\ell \bar{\nu}$ semi-leptonic form factors using Oktay-Kronfeld heavy quarks, we need to improve the heavy quark currents to the same level. We report our progress in calculating the improvement coefficients for currents composed of bottom and charm quarks.

Speaker: Mr Jaehoon Leem (Seoul National University)

Slides main.pdf

187 Isovector Axial Charge with Current Improvement

We employ dimension 4 operators to improve the local vector and axial vector currents, as the leading order approximation of the lattice conserved current, and then calculate the nucleon iso-vector axial coupling $g^3_A$ using overlap valence on Domain Wall Fermion sea. Using the equality of $g^3_A$ from $A_i$ and $A_4$ components of the axial-vector current as a normalization condition in addition to axial Ward identity, we find two to three percent increase of $g^3_A$ towards the experimental value. The excited state contamination has been taken into account with three time separations between the source and sink. The improved axial charges $g_A^{IM}(24I)=1.188(7)$, $g_A^{IM}(32I)=1.177(9)$ are obtained on $24^3\times 64$ and $32^3\times 64$ lattices at the unitary point where the pion masses are $330$ MeV and $300$ MeV respectively.

Speaker: Dr YIBO Yang (university of Kentucky)

188 Long-Distance Properties of Landau Gluon and Ghost Propagators and Deconfinement

We investigate numerically the long-distance properties of gluon and ghost propagators in Landau gauge on the lattice, for the SU(2) case. By considering electric and magnetic gluon propagators at nonzero temperature, we extract Debye screening masses and look for signs of deconfinement around the critical temperature. Our results are related to the zero-temperature behavior of infrared propagators for comparison.

Speaker: Tereza Mendes (University of São Paulo)

189 Momentum smearing

Hadrons in lattice QCD are usually created employing smeared interpolators. We introduce a new quark smearing that allows us to maintain small statistical errors and good overlaps of hadronic wavefunctions with the respective ground states, also at high spatial momenta. We test this method for various physical observables see also arXiv:1602.05525v2 [hep-lat].

Speaker: Mr Bernhard Lang (University Regensburg)

190 New extended interpolating fields for hadron correlation functions

We introduce new extended interpolating operators made of quenched three dimensional fermions propagating in the timeslices. Such non-local operators are well behaved under renormalisation. The mass of the three 3D fermions can be tuned in a controlled way to find a better overlap of the extended operators with the states of interest. We test these operators for baryon two-point functions and compare to point sources and Jacobi smearing.

Speaker: Mr Francesco Scardino (University of Rome "La Sapienza")

Poster conference_poster_6.pdf

191 New Noise Subtraction Methods in Lattice QCD

Lattice QCD calculations of quark loop operators are extremely time-consuming to evaluate. To calculate these diagrams we use stochastic noise methods, which employ a randomly generated set of noise vectors to project out physical signals. This is done with linear equation solvers like GMRES-DR (Generalized Minimum RESidual algorithm-Deflated and Restarted) for the first noise, and GMRES-Proj (similar algorithm projected over eigenvectors) for remaining noises. In this context, we are attempting to employ matrix deflation algorithms to reduce statistical uncertainty in these time-consuming lattice calculations. In addition, we are developing noise suppression algorithms using polynomial subtraction techniques, as well as combining deflation and polynomial methods in an original way.

Speaker: Mr Suman Baral (Baylor University)

Poster printhandler.pdf

192 Nucleon EDM from Chromo EDM using Domain-Wall Fermion

We present a progress report on the study of the CP violation effects on the nucleon from the quark chromoelectric dipole moment (cEDM) operator using $N_f=2+1$ dynamical Domain-Wall fermions. Details of the calculation and preliminary results for $m_\pi = 170$ and 250 MeV will be reported.

Speakers: Dr Hiroshi Ohki (RIKEN BNL Research Center), Sergey Syritsyn (Jefferson Lab)

193 O(4) scaling analysis in two-flavor QCD at finite temperature and density with improved Wilson quarks

We study scaling behavior of a chiral order parameter in the low density region, performing a simulation of two-flavor lattice QCD with improved Wilson quarks. It have been confirmed that the scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We discuss the scaling properties of the chiral phase transition at finite density, applying the reweighting method and calculating derivatives of the chiral order parameter with respect to the chemical potential. In the comparison between the scaling functions of the O(4) spin model and QCD at low density, there is a fit parameter which can be interpreted as the curvature of the chiral phase transition curve in the QCD phase diagram with respect to temperature and chemical potential. We determine the curvature of the phase boundary by the fitting. The physical scale is set by the gradient flow.

Speaker: Dr Takashi UMEDA (Hiroshima Univ.)

Poster Lattice2016_umeda.pdf

194 Perturbative running of the twisted Yang-Mills coupling in the gradient flow scheme

We present our ongoing computation of the running of the twisted Yang-Mills coupling using gradient flow techniques. In particular, we use the gradient flow equation with twisted boundary conditions to perform a perturbative expansion of the expectation value of the Yang-Mills energy density up to fourth order at finite flow time, and regularise the respective resulting sums and integrals. Additionally, we show our ongoing computation of the aforementioned integrals in the particular case of a two-dimensional twist.

Speaker: Mr Eduardo Ibanez Bribian (Instituto de Fisica Teorica UAM-CSIC)

Poster Lattice_2016.pdf

195 pMR: A high-performance communication library

On many parallel machines, the time LQCD applications spend in communication is a significant contribution to the total wall-clock time, especially in the strong-scaling limit. We present a novel high-performance communication library that can be used as a de facto drop-in replacement in existing software. Its lightweight nature that avoids some of the unnecessary overhead introduced by MPI allows us to improve the communication performance of an application without any algorithmic or complicated implementation changes. As a first real-world benchmark, we make use of the library in the coarse grid solve of the DD-\alphaAMG algorithm. On realistic lattices, we see an improvement of a factor 2x in pure communication time and total time savings of up to 20%.

Speaker: Mr Peter Georg (University of Regensburg)

Poster pMR.pdf

196 Prediction of positive parity Bs mesons and search for the X(5568)

We use a combination of quark-antiquark and $B^{(*)}K$ interpolating fields to predict the mass of two QCD bound states below the $B^*K$ threshold in the quantum channels $J^P=0^+$ and $1^+$. The mesons correspond to the b-quark cousins of the $D_{s0}^*(2317)$ and $D_{s1}(2460)$ and have not yet been observed in experiment, even though they are expected to be found by LHCb. In addition to these predictions, we obtain excellent agreement of the remaining p-wave energy levels with the known $B_{s1}(5830)$ and $B_{s2}^*(5840)$ mesons. The results from our first principles calculation are compared to previous model-based estimates. More recently the D0 collaboration claimed the existence of an exotic resonance $X(5568)$ with exotic flavor content $\bar{b}s\bar{d}u$. If such a state with $J^P=0^+$ exists, only the decay into $B_s\pi$ is open which makes a lattice search for this state much cleaner and simpler than for other exotic candidates involving heavy quarks. We conclude, however, that we do not find such a candidate in agreement with a recent LHCb result.

Speaker: Dr Daniel Mohler (Helmholtz-Institut Mainz)

Poster poster_mohler_embedded.pdf

197 Relaxation time of the fermions in the magnetic field (I) - the case for relativistic fermions -

The chiral magnetic effect (CME) is the quantum anomaly related electric charge transport phenomenon along the external magnetic field, which appears in various systems possessing chiral fermions, such as the quark-gluon plasma, condensed matter physics and astrophysics. The magnetic field dependence of the relaxation time is needed to compare the theory and experiments quantitatively. However, the model calculation of the relaxation time has been made by Argyres and Adams only for the non-relativisitic fermion with the strong magnetic field limit. In this poster, we extend the work by Argyres and Adams and compute the relaxation time for the relativistic fermions in the magnetic field.

Speaker: Ms Aya Kagimura (Osaka University)

Poster 211_kagimura.pdf

Wednesday, July 27

Algorithms and Machines

Convener: Prof. Mike Peardon

198 Domain decomposition and multilevel integration for fermions I

The numerical computation of many hadronic correlation functions is exceedingly difficult due to the exponentially decreasing signal-to-noise ratio with the distance between source and sink. Multilevel integration methods, using independent updates of separate regions in space-time, are known to be able to solve such problems but have so far been available only for pure gauge theory. We present first steps into the direction of making such integration schemes amenable to theories with fermions, by factorizing a given observable via an approximated domain decomposition of the quark propagator. This allows for multilevel integration of the (large) factorized contribution to the observable, while its (small) correction can be computed in the standard way.

Speaker: Stefan Schaefer (NIC, DESY)

Slides schaefer.pdf

199 Domain decomposition and multilevel integration for fermions II

The numerical computation of many hadronic correlation functions is exceedingly difficult due to the exponentially decreasing signal-to-noise ratio with the distance between source and sink. Multilevel integration methods, using independent updates of separate regions in space-time, are known to be able to solve such problems but have so far been available only for pure gauge theory. We present first steps into the direction of making such integration schemes amenable to theories with fermions, by factorizing a given observable via an approximated domain decomposition of the quark propagator. This allows for multilevel integration of the (large) factorized contribution to the observable, while its (small) correction can be computed in the standard way.

Speaker: Marco Cè (Scuola Normale Superiore, Pisa, Italy & INFN, Sezione di Pisa, Italy)

Slides slides.pdf

200 The DDalphaAMG solver library

In this talk we report on the publication of the DDalphaAMG solver library. We describe its features, show examples of its application and give an overview of future developments.

Speaker: Dr Matthias Rottmann (University of Wuppertal)

Slides rottmann.pdf

201 Adaptive Aggregation-based Domain Decomposition Multigrid for Twisted Mass Fermions

We extend the Adaptive Aggregation Based Domain Decomposition Multigrid (DD-$\alpha$AMG) algorithm to $N_f=2$ twisted mass fermions. We show numerical results for an $N_f=2$ ensemble of twisted fermions with a clover term simulated at the physical value of the pion mass. We fine-tuned the parameters to achieve a speedup comparable to the one obtained for clover fermions. We also present a complete analysis of the aggregation parameters that provides a novel insight on the multigrid methods for lattice QCD independently of the fermion discretization.

Speaker: Mr Simone Bacchio (University of Cyprus - University of Wuppertal)

Slides Bacchio.pdf

202 Domain Wall Fermion Simulations with the Exact One-Flavor Algorithm

As algorithmic developments have driven down the cost of simulating degenerate light quark pairs the relative cost of simulating single quark flavors with the Rational Hybrid Monte Carlo (RHMC) algorithm has become more expensive. TWQCD has proposed an exact one-flavor algorithm (EOFA) that allows for HMC simulations of a single quark flavor without taking a square root of the fermion determinant. We have independently implemented EOFA for Shamir and M\"{o}bius domain wall fermions, and begun to optimize and test our implementation against RHMC. In this talk we will discuss the derivation of the EOFA action, our tests of its equivalence to RHMC, and the current state of our implementation and optimization.

Speaker: Mr David Murphy (Columbia University)

Slides lattice_2016.pdf

203 A simple method to optimize HMC performance

We present a cheap strategy to optimize Hybrid Monte Carlo parameters in simulations of QCD and QCD-like theories. We specialize to the case of mass-preconditioning, with multiple-time-step Omelyan integrators. Starting from properties of the shadow Hamiltonian we show how the optimal setup for the integrator can be chosen once the forces and their variances are measured, assuming that those only depend on the mass-preconditioning parameter.

Speaker: Mr Andrea Bussone (Univeristy of Southern Denmark & CP3 Origins)

Slides talk.pdf

Applications Beyond QCD

Convener: Dr Nazario Tantalo (Rome University Tor Vergata and INFN sez. of Rome Tor Vergata)

204 Absence of bilinear condensate in three-dimensional QED

There are plausibility arguments that QED in three dimensions has a critical number of flavors of massless two-component fermions, below which scale invariance is broken by the presence of bilinear condensate. We present numerical evidences from our dynamical lattice simulations using overlap as well as Wilson-Dirac fermions for the absence of bilinear condensate using the following methods: finite-size scaling analysis of the low-lying eigenvalues of the Dirac operator, comparison of the eigenvalue distributions to the non-chiral random matrix theory, and by checking if the inverse participation ratio and number variance show ergodic behavior.

Speaker: Dr Nikhil Karthik (Florida International University)

Slides karthik.pdf

205 Finite size and infra-red effects in QCD plus QED

When QED is added to QCD simulations we have to consider the effects of massless degrees of freedom (the photons), which bring new problems which we did not have to worry about in simulations of pure QCD. Related to this, we have questions about the boundary conditions - how can we reconcile periodic boundary conditions with Gauss's Law? What is the best way of treating zero modes of the photon field? We combine data from our lattice simulations with perturbative calculations in the infra-red regime to gain insight into some of these questions.

Speaker: Dr Paul Rakow (University of Liverpool)

206 Infrared features of dynamical QED+QCD simulations

Using dynamical lattice simulations of the coupled theory of QED and QCD we explore some particular aspects of the periodic boundary conditions. We observe that the finite volume effects in spectroscopy are dependent upon the precise implementation of the gauge-fixing condition. We also report on the finite-volume dependence of the charge renormalisation.

Speaker: Dr Ross Young (University of Adelaide)

Slides Young-Latt16.pdf

207 Four-Fermion Theories with Exact Chiral Symmetry in Three Dimensions

We investigate a class of quantum field theories of fermions interacting by a quartic coupling. This includes well-known models like the Gross-Neveu model and the Thirring model. In three spacetime dimensions, these models are used to describe properties of solid state systems like high temperature superconductors and graphene. Additionally, they are interesting as toy models to study chiral symmetry breaking. The Gross-Neveu model always has a broken and a symmetric phase, while the existence of a broken phase in the Thirring model depends on the number of fermion flavours. The critical number of fermion flavours for chiral symmetry breaking is still subject of ongoing discussion. Using SLAC fermions, we are able to simulate the Thirring model with exact chiral symmetry, but the chiral condensate is not obtainable on a finite lattice without explicit breaking. The talk presents approaches to circumvent this problem. We use Fierz identities to transform the Thirring model into other four-fermion models, where the chiral condensate does not vanish. These models show a sign problem, which is not present in the original Thirring model. We present an algorithm inspired by fermion bags, which may overcome this short coming. As a second approach, the chiral symmetry breaking of a larger class of four-fermion models is studied.

Speaker: Mr Daniel Schmidt (Friedrich Schiller University Jena)

Slides main_talk_lattice16.pdf

208 Numerical simulation of Dirac semimetals

Dirac semimetals are recently discovered materials with low energy spectrum similar to the massless two flavour 3+1D Dirac fermions. The interaction between quasiparticles in Dirac semimetals is instantaneous Coulomb with large effective coupling constant \alpha\sim 1. In this report we present the result of study of the phase diagram of Dirac semimetals within lattice simulation with rooted staggered fermions. In particular, calculate the chiral condensate as a function of effective coupling constants and thus determine the position of semimetal-insulator transition in Dirac semimetals.

Speaker: Mr Andrey Kotov (ITEP)

Slides report.pdf

209 Competing order in the fermionic Hubbard model on the hexagonal graphene lattice

We study the phase diagram of the fermionic Hubbard model on the hexagonal lattice in the space of on-site and nearest neighbor couplings with Hybrid-Monte-Carlo simulations. With pure on-site repulsion this allows to determine the critical coupling strength for spin-density wave formation. We compare the standard approach of introducing a small mass term, explicitly breaking the sublattice symmetry, with a purely geometric mass, i.e. using lattices and boundary conditions such that the Dirac points fall in between the grid points inside the Brillouin zone without explicit sublattice-symmetry breaking. For the first method we extrapolate the corresponding susceptibility peaks towards zero mass and infinite volume in the usual way, while with the geometric mass only infinite volume extrapolation is needed. An added bonus is that it can be used with nearest neighbor repulsion and charge-density wave formation where the corresponding mass term would introduce a sign problem. The geometric mass thus provides a promising method to study the competition between these different types of order and the resulting phase diagram with ab-initio simulations.

Speaker: Prof. Lorenz von Smekal (Justus-Liebig University Giessen)

Slides LvS_July2016.pdf

Nonzero Temperature and Density

Convener: Dr Jaeger Benjamin (Swansea University)

210 Simulating low dimensional QCD on Lefschetz thimbles

Non-perturbative lattice QCD calculations at non-vanishing baryon number density are hampered by the sign problem. The path integral becomes highly oscillating and standard Monte Carlo techniques seize working. One possible solution is the Lefschetz thimble approach. It requires a deformation of the original integration domain into a manifold embedded in complex space. For properly chosen integration manifolds (``thimbles'') the sign problem is drastically alleviated. For some bosonic and fermionic models this approach has been shown to work. In this talk we will discuss aspects of the thimble discretization of low dimensional QCD.

Speaker: Dr Christian Schmidt (Universitaet Bielefeld)

Slides Schmidt_latt16.pdf

211 Lefschetz-thimble approach to the Silver Blaze problem of one-site fermion model

Path integral on Lefschetz thimbles gets much attention in the context of the sign problem, because of its usefulness in order to study the system with the complex classical action nonperturbatively. After giving its brief introduction, it is applied for studying the sign problem of the one-site Hubbard model. This model has a severe sign problem, which looks quite similar to that of the finite-density QCD at low temperatures. We present the analytical study of the sign problem using the Lefschetz-thimble method, and also discuss the failure of the complex Langevin method. Furthermore, we give a speculation about the early-onset problem of the baryon number density, called the baryon Silver Blaze problem, based on similarity between the sign problems of one-site Hubbard model and of finite-density QCD.

Speaker: Dr Yuya Tanizaki (RIKEN BNL Research Center)

Slides Tanizaki_Lattice2016.pdf

212 Talk withdrawn

213 Simulating thimble regularization of lattice quantum field theories (including LGT)

Monte Carlo simulations of lattice quantum field theories on Lefschetz thimbles are non trivial. We discuss a new Monte Carlo algorithm based on the idea of computing contributions to the functional integral which come from complete flow lines. The latter are the steepest ascent paths attached to critical points, i.e. the basic building blocks of thimbles. The measure to sample is thus dictated by the contribution of complete flow lines to the partition function. The algorithm is based on a heat bath sampling of the gaussian approximation of the thimble: this defines the proposals for a Metropolis-like accept/reject step. The effectiveness of the algorithm has been tested on a few models, e.g. the chiral random matrix model. We also discuss thimble regularization of gauge theories, and in particular the successfull application to 0+1 dimensional QCD and the status and prospects for Yang-Mills theories.

Speaker: Dr Francesco Di Renzo (University of Parma & INFN)

Slides fdrLAT2016.pdf

214 Complex spectrum of spin models for finite-density QCD

We consider the spectrum of transfer matrix eigenvalues associated with Polyakov loops in lattice QCD at strong coupling. The transfer matrix at finite density is non-Hermitian, and its eigenvalues become complex as a manifestation of the sign problem. We show that the symmetry under charge and complex conjugations ensures that the eigenvalues are either real or part of a complex conjugate pair, and the complex pairs lead to damped oscillatory behavior in Polyakov loop correlation functions, which also appeared in our previous phenomenological models using complex saddle points. We argue that the results reflect oscillatory behavior in color-charge densities and it should be observable in lattice simulations of QCD at finite density.

Speaker: Dr Hiromichi Nishimura (RIKEN BNL Research Center)

Slides Nishimura_Lattice2016.pdf

215 Study of the sign problem in canonical approach

Canonical approach is one of the powerful tools to approach the QCD phase diagram. We calculate the canonical partition function instead of the grand canonical one in the canonical approach. However, it is known that the sign problem emerges as a complex phase of the canonical partition function. Thanks to multi-precision calculations with the canonical approach we obtained the canonical partition function even for large baryon numbers. In this talk, we will argue the origin of this "phase", and study some behavior of its temperature and baryon number dependence.

Speaker: Asobu Suzuki (University of Tsukuba)

Slides 06_Suzuki.pdf

Standard Model Parameters and Renormalization

Convener: Prof. Francesco Knechtli (University of Wuppertal)

216 Non-perturbative matching of HQET heavy-light axial and vector currents in N_f=2 lattice QCD

Based on a non-perturbative matching strategy between Heavy Quark Effective Theory (HQET) at O(1/m) and finite-volume QCD, we report on our determination of the effective theory parameters of all components of the HQET heavy-light axial and vector currents in two-flavour lattice QCD. These parameters, which can be fixed by matching conditions between suitable QCD and HQET observables evaluated through numerical simulations, are required to absorb the power divergences of lattice HQET, as, for instance, encountered in an effective theory computation of form factors for semi-leptonic decays of B- and B_s-mesons.

Speaker: Dr Jochen Heitger (University of Muenster, ITP)

Slides lat16sl.pdf

217 Non perturbative renormalization of flavor singlet quark bilinear operators in lattice QCD

We report on our studies of the renormalization of flavor singlet quark bilinear operators in lattice QCD. The renormalization constants are determined non-perturbatively using gauge field ensembles with Nf=2 dynamical clover improved fermions. The renormalization is performed in the RI-MOM and RI-SMOM schemes. The difference between flavor singlet and non-singlet quark bilinear operators is a disconnected contribution, which has to be evaluated by stochastic estimators. We compare our results with perturbation theory.

Speaker: Dr Stefano Piemonte (University of Regensburg)

Slides presentazione.pdf

218 Non-Perturbative Renormalization of Nucleon Charges with Automated Perturbative Subtraction

We report on the determination of the renormalization factors of quark bilinears which are required among others in order to determine the nucleon scalar and tensor charges from the CLS $N_f=2$ configurations. Working in the RI'-MOM scheme, we eliminate all lattice artifacts at one-loop order using a combination of analytical results near the continuum limit and numerical calculations in automated lattice perturbation theory. The latter will allow for a ready generalization to the renormalization factors required for the average momentum fraction and other operators beyond local bilinears.

Speaker: Dr Georg von Hippel (University of Mainz)

Slides vonHippel.pdf

219 Non-perturbative determination of improvement coefficients using coordinate space correlators in Nf=2+1 lattice QCD

We determine quark mass dependent order a improvement terms of the form $b_J$ am for non-singlet scalar, pseudoscalar, vector and axialvector currents, using correlators in coordinate space. We use a set of CLS ensembles comprising non-perturbatively improved Wilson Fermions and the tree-level Luescher-Weisz gauge action at $\beta=3.4, 3.46, 3.55$ and $\beta=3.7$, corresponding to lattice spacings a in [0.05,0.09] fm. We report the values of the $b_J$ improvement coefficients which are proportional to non-singlet quark mass combinations and also discuss the possibility of determining the $\bar{b}_J$ coefficients which are proportional to the trace of the quark mass matrix.

Speaker: Dr Piotr Korcyl (University of Regensburg)

Slides lattice2016.pdf

220 A massive momentum-subtraction scheme

A new renormalization scheme is defined for fermion bilinears in QCD at non vanishing quark masses. This new scheme, denoted RI/mSMOM, preserves the benefits of the nonexceptional momenta introduced in the RI/SMOM scheme, and allows a definition of renormalized composite fields away from the chiral limit.

Speaker: Ms Ava Khamseh (The University of Edinburgh)

Slides lattice_2016_RImSMOM.pdf

Theoretical Developments

Convener: Masanori Hanada (Kyoto U, Stanford U)

221 Renormalisation of the scalar energy-momentum tensor with the Wilson flow

The Wilson flow is a promising tool to study strongly coupled theories. Its remarkable renormalisation properties allow for a meaningful formulation of the energy-momentum tensor on the lattice. The non-perturbative computation of the latter can in turn be used to study the scaling behaviour of quantum field theories. We extent recent studies on the renormalisation of the energy-momentum tensor in 4-dimensional gauge theory to the case of a 3-dimensional scalar theory to investigate its intrinsic structure and numerical feasibility on a more basic level. In this talk, we introduce the Wilson flow for scalar theory, discuss Ward identities, and present our results for the renormalisation constants of the scalar energy-momentum tensor.

Speaker: Susanne Ehret (University of Edinburgh)

Slides Susanne Ehret

222 Renormalization constants of the lattice energy momentum tensor using the gradient flow

We present an update about our program for the non perturbative renormalization of the energy momentum tensor. Our strategy consists in probing suitable lattice Ward identities with observables computed along the gradient flow. This set of identities exhibits many interesting qualities, arising from the UV finiteness of flowed composite operators, and can be used to measure the renormalization constants of the energy momentum tensor. We show how this method is applied in a SU(3) Yang-Mills theory on the lattice, and report our numerical results.

Speaker: Mr Francesco Capponi (Plymouth University)

Slides Seminar_EMT_wf_23-07-2016.pdf

223 The gradient flow coupling from numerical stochastic perturbation theory

The perturbative calculation of gradient flow observables is technically challenging. Current results are in fact limited to a few quantities and, in general, to low perturbative orders. Numerical stochastic perturbation theory is a potentially powerful tool that may be applied in this context. Precise results using these techniques, however, require control over both statistical and systematic uncertainties. In this talk we discuss how the recent algorithmic developments of these methods substantially ameliorate the cost for such precise computations. As an illustration we then present results for the two-loop matching of the gradient flow coupling in finite volume with Schroedinger functional boundary conditions and the $\overline{\rm MS}$ coupling.

Speaker: Dr Mattia Dalla Brida (DESY - Zeuthen)

Slides lat16.pdf

224 Continuing the Saga of Fluffy Mirror Fermions

I discuss continuing work on a recent proposal for the nonperturbative regulator for chiral gauge theories which combines domain wall fermions and gradient flow, Phys.Rev.Lett. 116 (2016) 211602. Implementing chiral gauge theories on the lattice requires not only decoupling mirror fermions to allow for fermions in complex representations, but also a road to failure for theories with fermions in anomalous representations. Unlike attempts to gap the mirror fermion spectrum, this proposal gives the mirror fermions exponentially soft form factors, allowing them to decouple from ordinary matter except through nontrivial gauge field topology. I discuss progress on various open questions for this formulation that were left unresolved in the original work.

Speaker: Ms Dorota Grabowska (INT/UW)

Slides GrabowskaNonPertRegLattice2016BetterForProjector.pdf GrabowskaNonPertRegLattice2016.pdf

225 Lattice Conformal Field theory on Curved Manifolds

A Quantum Finite Element (QFE) Lagrangian is formulated for a general simplicial complex approximation to a smooth Euclidean Riemann manifold. The construction is applied to Wilson Dirac fermions with the appropriate lattice spin connection and to phi 4th-theory with QFE counter terms required for these theories to converge in the continuum limit. Numerical tests are given for the Wilson-Fisher fixed point in 2D with comparison to the exact solution of the Ising CFT on the two sphere and for the 3D phi 4th-theory in radial quantization. Potential future applications to more general 3D conformal field theories and 4D Beyond the Standard Model (BSM) gauge theories near the conformal window are suggested.

Speaker: Prof. Richard Richard Brower (Boston University)

Slides QFE_Lat_2016.pdf

Weak Decays and Matrix Elements

Convener: Prof. Stefan Meinel (University of Arizona / RIKEN BNL Research Center)

226 Heavy-heavy current improvement for calculation of $\bar{B}\rightarrow D^{(*)}\ell \bar{\nu}$ semi-leptonic form factors using the Oktay-Kronfeld action -- 1

The Oktay-Kronfeld action is a highly improved version of the Fermilab action and systematically reduces heavy quark discretization effects through $\mathcal{O}(\lambda^3)$ in HQET power counting, for the heavy-light meson spectrum. To calculate $\bar{B}\rightarrow D^{(*)}\ell \bar{\nu}$ semi-leptonic form factors using Oktay-Kronfeld heavy quarks, we need to improve the heavy quark currents to the same level. We report our progress in calculating the improvement coefficients for currents composed of bottom and charm quarks.

Speaker: Dr Jon Bailey (Seoul National University)

Slides lattice16_bailey.pdf

227 $|V_{cb}|$ from $\bar{B}^0\rightarrow D^{*+} \ell^- \bar{\nu} $ zero-recoil form factor using 2$+$1$+$1 flavour HISQ and NRQCD

We present our recent calculation of the zero-recoil form factor for the semileptonic decay $\bar{B}^0\rightarrow D^{*+} \ell^- \bar{\nu} $ using lattice QCD with 2+1+1 flavours of highly improved staggered quarks in the sea (the MILC HISQ configurations) and using non-relativistic QCD for the bottom quark. We obtain $\mathcal{F}(1)$ and combine this with the latest HFAG average of $\eta_{EW} \mathcal{F}(1) |V_{cb}|$ to get a value for $|V_{cb}|$.

Speaker: Mr Judd Harrison (Department of applied mathematics and theoretical physics, University of Cambridge)

Slides Lattice2016JuddHarrison.pdf

228 B_c decays from highly improved staggered quarks and NRQCD

We use both non-relativistic QCD (NRQCD) and fully relativistic formalisms to calculate semileptonic form factors for the decays B_c -> eta_c lv and B_c -> J/psi lv over the entire q^2 range. To achieve this we employ a highly improved lattice quark action at several lattice spacings down to a=.044 fm, which allows a fully relativistic treatment of charm and simulation of the full q^2 range with controlled continuum extrapolation. We have two ways of treating the b quark: either with an O(alpha_s) improved NRQCD formalism or by extrapolating a heavy mass m_h to m_b in the relativistic formalism. Comparison of the two approaches provides an important cross-check of methodologies in lattice QCD. Nonperturbative renormalisation of the currents in the relativistic theory also allows us then to fix NRQCD-charm normalisation for b to c decays such as B -> D and B -> D^*.

Speaker: Dr Andrew Lytle (University of Glasgow)

Slides Lytle_Lattice2016.pdf

229 $B_{(s)}\to D_{(s)}$ semileptonic decays with NRQCD-HISQ valence quarks

We present a calculation of the form factors, $f_0$ and $f_+$, for the $B_{(s)}$ to $D_{(s)}$ semileptonic decays. Our work uses the MILC $n_f=2+1$ asqtad configurations with NRQCD and HISQ valence quarks at four values of the momentum transfer $q^2$. We present preliminary results for our combined chiral-continuum extrapolation.

Speaker: Dr Chris Monahan (Rutgers, the State University of New Jersey)

Slides cjmonahan_latt16.pdf

230 Semi-leptonic $B$ decays with charming final state

First results for our calculation of semi-leptonic $B$ decays with charmed-mesons in the final state are presented. Our work is based on RBC-UKQCD's 2+1 flavor domain-wall fermion and Iwasaki gauge field configurations, We calculate the form factors by simulating the $b$ quarks using the relativistic heavy quark action, create light $u/d$ and $s$ quarks with standard domain-wall kernel, and use optimised Möbius domain-wall fermions for charm quarks.

Speaker: Dr Oliver Witzel (University of Edinburgh)

Slides witzel_oliver.pdf

231 Calculation of hadronic matrix elements contributing to the $B_s-\bar{B}_s$ width difference

The width difference $\Delta \Gamma_s$ is one of three observables, along with the mass splitting $\Delta M_s$ and the semileptonic CP asymmetry $a^s_{\mathrm{SL}}$, whose measurements completely constrain the physics of $B_s-\bar{B}_s$ oscillations. One of the dominant uncertainties in theoretical calculations of the width difference is due to not knowing matrix elements of dimension-7 operators beyond the vacuum saturation approximation. In particular, progress requires a first-principles calculation of the matrix element of $R_2$, a $\Delta B = 2$ operator with a derivative acting on the strange quark field. We discuss our methodology and present preliminary results of a calculation of $\langle B_s | R_2 | \bar{B}_s\rangle$ using nonrelativistic $b$ quarks and highly-improved staggered $s$ quarks on the MILC Collaboration's $n_f = 2+1+1$ configurations.

Speaker: Dr Matthew Wingate (University of Cambridge)

Slides wingate_lattice2016.pdf

11:00 AM Coffee Break

Algorithms and Machines

Convener: Mr Guido Cossu (Higgs Centre for Theoretical Physics, School of Physics and Astronomy, University of Edinburgh)

232 Optimization of the Domain Wall Dslash Kernel in Columbia Physics System

We present updated strategies and results of combining hand-tuning with the R-Stream source-to-source auto-parallelizing compiler to transform the serial implementation of the domain wall fermion Dslash kernel in CPS into an efficient parallel code targeting the Intel Xeon CPUs. The R-Stream compiler performs preliminary optimizations of the input Dslash code, including a novel iteration space compression scheme, while the SIMD optimization is done with a data layout transformation and compiler intrinsics. Tuning for the OpenMP and MPI scaling will also be discussed.

Speaker: Dr Meifeng Lin (Brookhaven National Laboratory)

Slides MLin_LAT2016.pdf

233 Algorithms for disconnected diagrams.

Computing disconnected diagrams on the lattice involves taking the trace of the inverse of the Dirac operator. This is a computationally challenging problem, however recent algorithmic improvements such as low mode averaging and hierarchical probing have increased the efficiency of this trace estimation. We detail an algorithm that builds upon hierarchical probing by deflating the near null space of the Dirac matrix. An additional order of magnitude of variance reduction is achieved by combining these two methods and we explore this synergy both theoretically and experimentally. Finally, we apply this algorithm to calculate contributions to the Pauli and Dirac form factors of the nucleon, and present initial results.

Speaker: Mr Arjun Gambhir (College of William and Mary/JLab)

Slides gambhir_lattice2016_final.pdf

234 A method to compute derivatives of functions of large complex matrices

We present a method for the numerical calculation of derivatives of functions of general complex matrices which also works for implicit matrix function approximations such as Krylov-Ritz type algorithms. An important use case for the method is the overlap Dirac operator at finite quark chemical potential. The evaluation of the overlap Dirac operator at finite chemical potential calls for the computation of the product of the sign function of a non-Hermitian matrix with some source vector. For non-Hermitian matrices the sign function can no longer be efficiently approximated with polynomials or rational functions. Instead one invokes implicit approximation algorithms, like Krylov-Ritz methods, that depend on the source vector. Our method allows for an efficient calculation of the derivatives of such implicit approximations, which is necessary for the computation of conserved lattice currents or the fermionic force in Hybrid Monte-Carlo or Langevin simulations. We also give an explicit deflation prescription for the case when one knows several eigenvalues and eigenvectors of the matrix being the argument of the differentiated function. To show that the method is efficient and well suited for practical calculations we provide test results for the two-sided Lanczos approximation of the finite-density overlap Dirac operator on $SU(3)$ gauge field configurations on lattices with sizes up to $ 14\times14^3 $

Speaker: Mr Matthias Puhr (University of Regensburg)

Slides lattice2016_puhr.pdf

Chiral Symmetry

Convener: Dr Stephan Durr (University of Wuppertal)

235 Comparing different definitions of the topological charge

We perform a numerical comparison of different lattice definitions of the topological charge by investigating the correlation coefficient between different definitions as well as the topological susceptibility. We use small-volume ensembles with 2 flavours of dynamical twisted mass fermions. We investigate the following definitions of the topological charge: index of the overlap Dirac operator, spectral flow of the Hermitian Wilson-Dirac operator, spectral projectors and field theoretic extracted with the smoothing schemes of APE, stout and HYP smearing schemes as well as cooling and the recently introduced gradient flow. Furthermore, we carry out a (tree-level) perturbative comparison between the smoothing procedures of the gradient flow, cooling as well as APE and stout smearing. We demonstrate both analytically and numerically that the above smoothing schemes are equivalent if the smoothing scales (flow time, number of cooling or smearing steps) are rescaled properly. Moreover, we demonstrate that HYP smearing is numerically equivalent with all the above smoothers. We show that the generally high correlation between different definitions increases towards the continuum limit.

Speaker: Dr Andreas Athenodorou (University of Cyprus)

Slides presentation.pdf

236 $\theta$-dependence of the massive Schwinger model

Understanding the role of the $\theta$ parameter in QCD and its connection with the strong CP problem and axion physics is one of the major challenges for high energy theorists. Due to the sign problem, at present only the QCD topological susceptibility is well known. Using an algorithmic approach that could potentially be extended to QCD, we study as a first step the $\theta$-dependence in the massive Schwinger model, and try to verify a conjecture of Coleman.

Speaker: Eduardo Royo (Universidad de Zaragoza)

Slides massiveSchwinger.pdf

237 Real-time simulations of anomaly induced transport in external magnetic field

One of the macroscopic manifestations of the Chiral anomaly in a matter with Dirac fermions is a large negative magnetoresistivity in strong magnetic fields, which is common feature of Weyl- and Dirac semimetals and QCD. However, most of previous studies have been done in the linear response approach in non-interacting theory. We study Magnetoresistivity in a model of Dirac semimetal using Wilson-Dirac lattice fermions with on-site four-fermion interactions in the background of magnetic field in the framework of mean-field theory and classical-statistical real-time simulations with arbitrary external electric fields. We investigate the phase diagram of the model and discuss the fate of dynamically generated chiral imbalance in the system, as well as manifestations of dynamical axion field.

Speaker: Mr Senia Valgushev (Regensburg University)

Slides Valgushev_Lattice2016.pdf

Nonzero Temperature and Density

Convener: Dr Denes Sexty (Uni Wuppertal)

238 Equation of state in (2+1)-flavor QCD with gradient flow

The energy-momentum tensor and the equation of state are studied in finite-temperature (2+1)-flavor QCD with improved Wilson quarks, using the gradient flow method proposed by Makino and Suzuki. Although the up and down quarks are heavy yet ($m_{\rm PS}/m_V \approx 0.63$), we obtain reasonable results, suggesting that the method works well. We also report on the results on the chiral condensate and its susceptibility with the gradient flow method.

Speaker: Prof. Kazuyuki Kanaya (CiRfSE, Univ. Tsukuba)

Slides 160727_kanaya-lat.pdf

239 The QCD equation of state at finite density from analytical continuation

An efficient way to study the QCD phase diagram at small finite density is to extrapolate thermodynamical observables from imaginary chemical potential. In this talk we present results on several observables for the equation of state to order (muB/T)^6. The observables are calculated along the isentropic trajectories in the (T, muB ) plane corresponding to the RHIC Beam Energy Scan collision energies. The simulations are performed at the physical mass for the light and strange quarks. muS was tuned in a way to enforce strangeness neutrality to match the experimental conditions; the results are continuum extrapolated using lattices of up to Nt = 16 temporal resolution.

Speaker: Ms Jana Günther (University of Wuppertal)

Slides talk_guenther.pdf

240 Phase diagram of the O(3) model from dual lattice simulations

We simulated the asymptotically free two-dimensional O(3) model at nonzero chemical potential through dual variables free of the sign problem. The system undergoes a quantum phase transition when mu reaches the particle mass (generated dynamically similar to QCD). The density follows a square root universal for repulsive bosons in one spatial dimension. We have also measured the spin stiffness, known to be sensitive to the spatial correlation length, in different scaling trajectories to zero temperature and infinite size. It points to a dynamical critical exponent z=2, which can be explained by particle worldlines. Comparisons to thermodynamic Bethe ansaetze are shown as well.

Speaker: Dr Falk Bruckmann (University of Regensburg)

Slides bruckmann_south_newer.pdf

Physics Beyond the Standard Model

Convener: Prof. Joel Giedt (Rensselaer Polytechnic Institute)

241 SUNny gluonia as DM

We investigate the possibility that the dark matter candidate is from a pure non-abelian gauge theory of the hidden sector, motivated in large part by its elegance and simplicity. The dark matter is the lightest bound state made of the confined gauge fields, the hidden glueball. We point out this simple setup is capable of providing rich and novel phenomena in the dark sector, especially in the parameter space of large $N$. They include self-interacting and warm dark matter scenarios, Bose-Einstein condensation leading to massive dark stars possibly millions of times heavier than our sun giving rise to gravitational lensing effects, and indirect detections through higher dimensional operators as well as interesting collider signatures. Non-perturbative relevant studies to further our understandings of these uniquely simple non-abelian gauge theories are suggested. This talk is based on arXiv:1602.00714 [to appear in Phys. Rev. D] with Yue Zhang [CIT] and more in progress with him.

Speaker: amarjit soni (BNL)

Slides LAT16_final.pdf

242 dark matter from one-flavor SU(2) gauge theory

SU(2) gauge theory with a single fermion in the fundamental representation is a minimal non-Abelian candidate for the dark sector. Having only a single flavor provides a natural mechanism for stabilizing dark matter on cosmological timescales. Preliminary lattice results will be presented and discussed in the context of dark matter phenomenology.

Speaker: Randy Lewis (York University)

Slides lewis.pdf

Theoretical Developments

Convener: Prof. Wosiek Josef

243 Volume reduction through perturbative Wilson loops

We derive the perturbative expansion of Wilson loops to order g^4 in a SU(N) lattice gauge theory with twisted boundary conditions. Our expressions show that the thermodynamic limit is attained at infinite N for any number of lattice sites and allow to quantify the deviations from volume independence at finite large N as a function of the twist. The effect of adjoint Wilson fermions will be briefly described.

Speaker: Prof. Margarita Garcia-Perez (Instituto de Fisica Teorica UAM-CSIC)

Slides garcia_perez.pdf

244 Meson masses and decay constants at large N

Meson masses and decay constants in the large N limit of SU(N) gauge theory is estimated from the twisted space-time reduced model. To this end, we introduce a new smearing method which enables us to obtain reliable values for these quantities.

Speaker: Prof. Masanori Okawa (Hiroshima University)

Slides okawa.pdf

245 't Hooft model on the lattice

We use a recently formulated expression for computing meson masses at large N to study the spectrum of two-dimensional QCD in the large N limit. The model serves as a testing ground to explore methodology of meson mass determination with different techniques and versions of lattice fermions.

Speaker: Prof. Antonio Gonzalez-Arroyo (Instituto de Fisica Teorica UAM/CSIC)

Slides talk_lattice.pdf

Weak Decays and Matrix Elements

Convener: Dr Takashi Kaneko (KEK)

246 Current correlators in the coordinate space at short distances

We calculate the current correlators in the coordinate space and compare them with the experimental information obtained through the spectral functions of hadronic tau decays at ALEPH. Lattice data are obtained with 2+1 Mobius domain-wall fermions at three lattice spacings 0.044, 0.055 and 0.080 fm and the continuum limit is taken. On the experimental side, there is no information for the spectral functions above the tau lepton mass and one usually assumes that the perturbation theory is applicable there. Through the comparison with the lattice data, we are able test the validity of this quark-hadron duality assumption to some extent.

Speaker: Mr Masaaki Tomii (SOKENDAI)

Slides Lattice2016.pdf

247 Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite volume effects.

In Ref.[1] we proposed a method for calculating leptonic (and semileptonic) decay rates of pseudoscalar mesons including $O(\alpha)$ electromagnetic corrections. Because of the presence of infrared divergences, this requires the calculation of contributions with both virtual and real photons. We have shown that the real photon contribution, by integrating up to photon momenta of the order of 20-30 MeV, can be calculated by treating the meson as a point-like particle. The corrections to this approximation are negligible because a very soft photon cannot resolve the internal structure of the hadron. For the virtual contribution we need to integrate over all photon momenta and the point-like effective theory is not a valid approximation. For this reason we proposed to compute the virtual contribution by a non-perturbative lattice simulation. The logarithmic infrared divergences are properly regulated by the finite volume and are cancelled by subtracting from the non-perturbative lattice results the virtual decay rate calculated in the point-like approximation. In this talk we discuss two main analytic results. First we give the explicit analytical expression of the finite volume virtual decay rate in the point-like approximation, necessary for the cancellation of the infrared divergences. We also show explicitly that the $O(1/L)$ finite volume corrections (FVC) to the virtual decay rate are universal, i.e. they are the same in the full theory and in the point-like effective theory. They therefore cancel in the difference of the non-perturbative decay rate and that in the point-like approximation. Structure dependent terms start to contribute to the FVC at $O(1/L^2)$ only. With the theoretical results discussed in this talk all the ingredients are now in place to compute the decay rates at $O(\alpha)$. The numerical results from an exploratory non-perturbative lattice calculation will be presented by S. Simula in a companion talk. [1]. N. Carrasco et al., Phys. Rev. D91 (2015) 074506.

Speaker: Dr Nazario Tantalo (Rome University Tor Vergata and INFN sez. of Rome Tor Vergata)

Slides presentation.pdf

248 Electromagnetic corrections to the leptonic decay rates of charged pseudoscalar mesons: lattice results

Electromagnetic effects on the leptonic decay rates pi+ -> mu+ nu and K+ -> mu+ nu are evaluated for the first time on the lattice. Following a method recently proposed in Ref. [1] the emission of virtual photons at leading order in the e.m. coupling is evaluated on the lattice with the subtraction of the infrared divergence computed for a point-like meson at finite lattice volume. The physical decay rate is then obtained by adding the emission of real photons regularized with a photon mass. Using the gauge ensembles produced by ETMC with Nf=2+1+1 dynamical quarks the feasibility of the lattice approach is demonstrated and preliminary results for the decay rates of charged pion and kaon will be presented. [1]. N. Carrasco et al., Phys. Rev. D91 (2015) 074506.

Speaker: Dr Silvano Simula (INFN - Roma Tre)

Slides Simula_LAT16.pdf

Excursion

Thursday, July 28

Plenary Session

Convener: Prof. Junko Shigemitsu (OSU)

249 Impact of lattice QCD on CKM phenomenology

In this talk I review the implications of recent lattice QCD results on the phenomenology of flavour and CP-violating meson decays. Precise lattice QCD results for hadronic matrix elements, decay constants and form factors play a crucial role in the determination of CKM matrix elements and in the identification of possible new physics contributions to flavour violating observables. I also highlight some possible future directions for lattice QCD calculations which would have a big impact on flavour phenomenology.

Speaker: Monika Blanke (Karlsruhe Institute of Technology)

Slides Blanke-Lattice16.pdf

250 Heavy flavor physics

Heavy meson decays are used to extract the fundamental parameters in Standard Model such as CKM matrix elements and probe new physics beyond the Standard Model. Lattice QCD provides a non-perturbative method to calculate the matrix elements in these processes. In this talk, I will review recent progress in the study of B and D meson decay constants, semileptonic decay form factors, B and D meson mixing. In addition, I will present the impact of lattice-QCD results on phenomenology and compare the latest Standard Model predictions with the experimental results.

Speaker: ran zhou (Fermi National Accelerator Laboratory)

Slides Flavor_phy.pdf

251 Neutrinoless double beta decay from lattice QCD

While the discovery of non-zero neutrino masses is one of the most important accomplishments by physicists in the past century, it is still unknown how and in what form these masses arise. Lepton number-violating neutrinoless double beta decay is a natural consequence of Majorana neutrinos and many BSM theories, and several experimental efforts are involved in the search for these processes. Understanding how neutrinoless double beta decay would manifest in nuclear environments is key for understanding any observed signals. In this talk I will present an overview of a set of one- and two-body matrix elements relevant for experimental searches for neutrinoless double beta decay, along with preliminary lattice QCD results.

Speaker: Dr Amy Nicholson (UC Berkeley)

Slides Lattice20160nuBB.pdf

10:45 AM Coffee Break

Plenary Session

Convener: Dr Andreas Kronfeld (Fermilab)

252 QED Corrections to Hadronic Observables

When aiming at a percent precision in hadronic quantities calculated by means of lattice simulations, isospin breaking effects become relevant. These are of two kinds: up/down mass splitting and electromagnetic corrections. In order to properly account for the latter, a consistent formulation of electrically-charged states in finite volume is needed. In fact on a periodic torus Gauss' law and large gauge transformations forbid the propagation of electrically-charged states. In this talk I will review methods that have been used or proposed so far in order to circumvent this problem, while highlighting practical as well as conceptual pros and cons. I will also review and discuss various methods to calculate electromagnetic corrections to hadron masses and decay rates in numerical simulations.

Speaker: Agostino Patella (CERN and Plymouth U.)

Slides patella.pdf

253 Presentation of 2016 Kenneth Wilson Award

12:30 PM Lunch Break

Algorithms and Machines

Convener: Prof. Tilo Wettig

254 Introduction to the Quantum EXpressions (QEX) framework

We present a new lattice field theory software framework designed with ease of use, flexibility, efficiency and portability in mind. The framework is written using the Nim programming language which offers many of the features one would find in a high-level scripting language, while in fact being a strongly-typed language with full control over low-level optimizations. This allows us to present a simple expression-based language to the end user that can be transformed into highly optimized code for a particular architecture. We will discuss the features of the QEX framework, performance results and development plans.

Speaker: Dr James Osborn (ANL)

Slides talk.pdf

255 Block Solver for multiple right hand sides on NVIDIA GPUs

Analysis tasks in Lattice QCD often requires solving linear equations for multiple right hand sides for a constant gauge field. Recently deflation methods have become more widely used and proven to be very efficient. They however do require the calculation and storing of eigenvectors which is either not always feasible or too expensive. Here we present results for an implementation of a block solver for multiple right hand sides using the QUDA library for QCD on NVIDIA GPUs. By making use of the gauge field reuse in the Dslash operator, mixed precision approaches and block Krylov space methods they do provide outstanding solver performance. We present results on NVIDIA's most recent Pascal architecture.

Speaker: Dr Mathias Wagner (NVIDIA)

Slides Lattice2016_MathiasWagner.pdf

256 Accelerating Lattice QCD Multigrid on GPUs Using Fine-grained Parallelization

The past decade has witnessed a dramatic acceleration of lattice quantum chromodynamics calculations in nuclear and particle physics. This has been due to both significant progress in accelerating the iterative linear solvers using multi-grid algorithms, and due to the throughput improvements brought by GPUs. Deploying hierarchical algorithms optimally on GPUs is non-trivial owing to the lack of parallelism on the coarse grids, and as such, these advances have not proved multiplicative. Using the QUDA library, we demonstrate that by exposing all sources of parallelism that the underlying stencil problem possesses, and through appropriate mapping of this parallelism to the GPU architecture, we can achieve high efficiency even for the coarsest of grids. Results are presented for the Wilson-clover discretization, where we demonstrate up to 10x speedup over present state-of-the-art GPU-accelerated methods on Titan. Finally, we consider how the combination of multigrid, NVIDIA's new Pascal architecture and block Krylov solvers result in a multiplicative speedup of 100x versus prior GPU state of the art.

Speaker: Dr Kate Clark (NVIDIA)

Slides lattice_2016.pdf

257 Progress Report on Staggered Multigrid

As the push towards the exascale enables increasingly accurate lattice calculations, the inversion of the Dirac matrix becomes a superlinearly growing expense. Adaptive algebraic multigrid (AAMG) methods for all fermion discretizations are essential to address this phenomena of critical slowing down. As a preconditioner, AAMG expedites Dirac matrix inversions with manageable start up costs. This is important for modern lattice measurements which require the efficient computation of an increasing number of Dirac propagators. In this talk we will discuss progress towards the development of an AAMG algorithm for staggered fermions based upon the successful implementation of Wilson-Clover multigrid. Optimal performance is being sought in the QUDA library on GPUs.

Speaker: Dr Evan Weinberg (Boston University)

Slides weinberg-evan-stag-mg.pdf

258 A performance evaluation of CCS QCD Benchmark on Intel Xeon Phi (KNC) systems

The most computationally demanding part of Lattice QCD simulations is solving quark propagators. Quark propagators are typically obtained with a linear equation solver utilizing HPC machines. The success of Lattice QCD simulations owes much to the development of numerical algorithms and optimization for the quark solver, and evolution of HPC machines. The CCS QCD Benchmark is a benchmark program solving the Wilson-Clover quark propagator, and is developed at Center of Computational Sciences (CCS), University of Tsukuba. This is designed to be as simple as possible and is written in plain Fortran 90 so that new algorithms or new HPC architectures can be evaluated quickly with this benchmark program. We optimized the benchmark program for a Intel Xeon Phi (Knights Corner, KNC) system named "COMA (PACS-IX)" at CCS Tsukuba under the Intel Parallel Computing Center program. A single precision BiCGStab solver with the overlapped Restricted Additive Schwarz (RAS) preconditioner was implemented using SIMD intrinsics, OpenMP and MPI in the offload-mode. In this talk, we will show the optimization methods and the performance of the CCS QCD benchmark on the COMA system.

Speaker: Dr Ken-Ichi Ishikawa (Hiroshima University)

Slides Lat2016_CCSQCDbench.pdf

259 MILC Staggered Conjugate Gradient Performance on Intel KNL

We review our work done to optimize the staggered conjugate gradient(CG) algorithm in the MILC code for use with the Intel Knights Landing (KNL) architecture. KNL is the second generation Intel Xeon Phi processor. It is capable of massive thread parallelism, data parallelism and high on-board memory bandwidth, and is being adopted in supercomputing centers for scientific research. The CG solver consumes the majority of time in production running, so we have spent most of our effort on it. We compare performance of an MPI+OpenMP baseline version of the MILC code with a version incorporating the QPhiX staggered CG solver, for both one-node and multi-node runs.

Speaker: Dr Ruizi Li (Indiana University)

Slides Lattice2016.pdf

Hadron Spectroscopy and Interactions

Convener: Prof. Gunnar Bali (University of Regensburg)

260 Charm physics by $N_f=2+1$ Iwasaki gauge and the six stout smeared $O(a)$-improved Wilson quark actions on a $96^4$ lattice

We present our results of charm physics in $N_f=2+1$ lattice QCD. Our calculation is performed on configurations generated with Iwasaki gauge and the six stout smeared $O(a)$-improved Wilson quark actions on a $96^4$ lattice at $\beta=1.82$ ($a^{-1} = 2.3$ GeV) with the spatial extent $L=8.1$ fm. The pion mass is almost physical $m_\pi=145$~MeV. The relativistic heavy quark action is utilized for the charm quark. We exhibit the charmed spectrum and the charm quark mass, focusing on stout smearing influence.

Speaker: Yusuke Namekawa (University of Tsukuba)

Slides namekawa-2016_07_28.pdf

261 Spectroscopy of charmed mesons from lattice QCD

Charmed meson spectroscopy with data generated by the Hadron Spectrum Collaboration is presented, using two ensembles with different light sea-quark masses to investigate the effect of the sea quark mass on the spectrum. Initial results from an investigation of the contribution of the disconnected quark-line diagram on the charmonium hyperfine splitting will be presented, including a comparison with quenched data.

Speaker: Mr David Tims (Trinity College Dublin)

Slides Southamptontalk.pdf

262 Impact of dynamical charm quarks

We investigate the influence of dynamical charm quarks on various observables. For observables without explicit charm-quark dependence, decoupling applies and the effects are expected to be small. However, we also study quantities with explicit charm-quark dependence, like the charmonium mass spectrum, where decoupling does not apply. Our study puts an emphasis on careful continuum extrapolations, which require very small lattice spacings when heavy quarks are present in the action. Since our precision goals cannot be currently met in full QCD, we carry our investigations out in a model without light quarks; quenched QCD is compared to QCD with two dynamical heavy quarks.

Speaker: Dr Tomasz Korzec (Bergische Universität Wuppertal)

Slides lat.pdf

263 Coupled-channel analysis of $D\pi$, $D\eta$ and $D_{s}\bar{K}$ scattering using lattice QCD

We present an extensive study of isospin $1/2$ coupled-channel $D\pi$, $D\eta$ and $D_{s}\bar{K}$ scattering, as well as isospin $3/2$ elastic $D\pi$ scattering, from $N_{f} = 2+1$ lattice QCD. Our use of distillation in combination with variationally optimised interpolating operators allows us to extract statistically precise two-meson spectra, which we use to constrain scattering amplitudes as a function of energy. We interpret our results in terms of poles in the scattering matrix, finding a near-threshold bound state in S-wave, a deeply bound vector state in P-wave and a narrow resonance in D-wave.

Speaker: Dr Graham Moir (University of Cambridge)

Slides G.Moir_lattice_2016.pdf

264 Charm-strange mesons and D K scattering

I will discuss a recent lattice QCD investigation of $D$ $K$ scattering relevant for near-threshold charm-strange mesons such as the enigmatic $D_s(2317)$. By employing a range of techniques we extracted precise finite-volume spectra in a number of different channels. These were used to map out the energy dependence of the scattering phase shift and from the singularity structure of the scattering amplitude we determined the resonant and bound state content. I will conclude with some comments on future prospects.

Speaker: Dr Christopher Thomas (University of Cambridge)

Slides Lattice2016_Thomas.pdf

265 Near threshold states $D_{s0}^{*}\left(2317\right)$ and $D_{s1}\left(2460\right)$

Early theoretical studies and lattice simulations predicted the charmed-strange mesons $D_{s0}^{*}(2317)$ and $D_{s1}(2460)$ to be broad states lying above the thresholds, $DK$ and $D^{*}K$, respectively. Experiments found narrow states below threshold. We present results of a high statistics $Nf=2$ study with a lattice spacing of approximately $0.071$ fm, taking explicitly into account the thresholds by including four quark operators. We find a lowering of the meson’s masses relative to the two-quark operator results. Two pion masses with multiple volumes were employed, $Lm_{\pi}=2.5,3.4,4.2$ and $6.7$ at $m_{\pi}=289$ MeV and $Lm_{\pi}=2.8$ and $3.5$ at $m_{\pi}=150$ MeV. The volume dependence of the resulting spectrum is investigated according to Luescher’s formula.

Speaker: Mr Antonio Cox (University of Regensburg)

Slides Cox_Lattice.pdf

Hadron Structure

Convener: Dr Christian Wiese (NIC - DESY Zeuthen)

266 Charge radii and higher electromagnetic moments with lattice QCD in nonuniform background fields

Nonuniform background electromagnetic fields, once implemented in lattice QCD calculations of hadronic systems, provide a means to constrain a large class of electromagnetic properties, from higher electromagnetic moments and charge radii to electromagnetic form factors. In this talk, I present the recent theoretical developments in realizing general background fields in periodic hypercubic lattices, along with a numerical illustration of the formalism. Additionally, I will briefly explain the formal procedure that allows the extraction of the charge radius and the quadruple moment of hadrons and light nuclei by matching an appropriate effective hadronic theory to lattice QCD correlation functions in a linearly varying electric field in space.

Speaker: Dr Zohreh Davoudi (MIT)

Slides LQCD-with-background-fields-Davoudi-v.1.0.pdf

267 A high-statistics lattice QCD study of nucleon sigma terms

For the Budapest-Marseille-Wuppertal collaboration We present a lattice study of the u, d and s quark contents of the nucleon, determined using the Feynman-Hellmann theorem. Results are obtained from twenty-nine high-statistics simulations with four flavors of O(a)-improved Wilson quarks, four lattice spacings and a variety of quark masses.

Speaker: Dr Laurent Lellouch (CNRS & Aix-Marseille U.)

Slides talk.pdf

268 Form factors from moments of correlation functions

Momentum-space derivatives of matrix elements can be related to their coordinate-space moments through the Fourier transform. We derive these expressions as a function of momentum transfer $Q^2$ for asymptotic in/out states consisting of a single hadron. We calculate corrections to the finite volume moments by studying the spatial dependence of the lattice correlation functions. This method permits the computation of not only the values of matrix elements at momenta accessible on the lattice, but also the momentum-space derivatives, providing *a priori* information about the $Q^2$ dependence of form factors. As a specific application we use the method, at a single lattice spacing and with unphysically heavy quarks, to directly obtain the slope of the isovector form factor at various $Q^2$, whence the isovector charge radius. The method has potential application in the calculation of any hadronic matrix element with momentum transfer, including those relevant to hadronic weak decays.

Speaker: Dr Chia Cheng Chang (LBNL)

Slides lat16_chang.pdf

269 Nucleon Vector and Axial-Vector Form Factors

We present the status of the calculation of the nucleon iso-vector axial and vector form factor using the MILC $N_f=2+1+1$ HISQ ensembles with lattice spacings $a=0.12, 0.09$, and $0.06\;\mathrm{fm}$ and three values of light quark masses corresponding to pion masses $310, 220, 130\;\mathrm{MeV}$. Valence quarks are simulated with the clover action. A number of techniques to increase the statistics cost effectively, such as the AMA (all-mode-averaging) method, will be discussed.

Speaker: Dr Yong-Chull Jang (Los Alamos National Laboratory)

Slides main.pdf

270 Computing the nucleon Dirac radius directly at $Q^2=0$

We describe a lattice approach for directly computing momentum derivatives of nucleon matrix elements using the Rome method, which we apply to obtain the isovector magnetic moment and Dirac radius. We present preliminary results calculated at the physical pion mass using a 2HEX-smeared Wilson-clover action from the Budapest-Marseille-Wuppertal collaboration. For removing the effects of excited-states contamination, the calculations were done at three source-sink separations and the summation method was used.

Speaker: Nesreen Hasan (Bergische Universitaet Wuppertal)

Slides talk_hasan.pdf

271 Light and strange axial form factors of the nucleon at pion mass 317 MeV

A lattice QCD calculation of the light and strange axial form factors $G_A$ and $G_P$ of the nucleon will be reported. Disconnected diagrams were calculated using hierarchical probing, and a clear nonzero signal was obtained. We pay special attention to renormalization, which we determined nonperturbatively, including the mixing between light and strange quarks. This calculation was done on a single ensemble with 2+1 flavours of stout-smeared Wilson-clover fermions at pion mass 317 MeV and near-physical strange quark mass.

Speaker: Dr Jeremy Green (Institut für Kernphysik, Johannes Gutenberg-Universität Mainz)

Slides slides.pdf

Nonzero Temperature and Density

Convener: Prof. Edwin Laermann (Bielefeld University)

272 Open charm correlators and spectral functions at high temperature

We present results for correlators and spectral functions of open charm mesons using 2+1 flavours of clover fermions on anisotropic lattices. The D mesons are found to melt close to the deconfinement crossover temperature $T_c$. Our preliminary results suggest a shift in the thermal D meson mass below $T_c$.

Speaker: Dr Jon-Ivar Skullerud (Maynooth University)

Slides Dmesons.pdf

273 Charm quark diffusion coefficient from nonzero momentum Euclidean correlator in temporal channel

We study the charm quark diffusion coefficient from nonzero momentum correlator in temporal channel on the quenched lattice. Euclidean correlator in temporal channel with zero momentum is constant as a function of the imaginary time because of the charge conservation. However this quantity with finite momentum is dependent on imaginary time and is more sensitive to the low energy structure of the spectral function than those in the spatial channel. We make estimates on the diffusion coefficient from this channel. We perform the numerical simulation on the lattice and apply the discussion for 1.5　< T/T_c<4.5.

Speaker: Mr Atsuro Ikeda (Osaka University)

Slides lattice2016.pdf

274 Stochastic approaches to extract spectral functions from Euclidean correlators

The spectral functions provide us the knowledge to understand the in-medium hadron and transport properties of the QCD medium. For instance, quantities like thermal dilepton production and photon emission rates of QGP can be obtained from the vector spectral functions. Though spectral functions are important, they can not be obtained directly from Euclidean lattice QCD calculations. Analytic continuations to real time are needed to extract spectral functions from Euclidean correlation functions. Currently the most commonly used method is the Maximum Entropy Method (MEM). To investigate the systematic uncertainties in spectral function reconstructions we study two stochastic approaches, i.e. Stochastic Optimization Method (SOM) and Stochastic Analytical Inference (SAI). SOM has advantage that it does not need any prior information. SAI is more generalized method, which reduces to the MEM in the mean-field limit. We compare results obtained from these two methods with those from MEM by investigating various model correlation functions.

Speaker: Mr Haitao Shu (CCNU)

Slides SOM_SAI_SHU.pdf

275 Stochastic reconstruction of charmonium spectral functions at finite temperature

We study charmonium spectral functions at finite temperature by using stochastic reconstruction methods. Our quenched lattice QCD simulations are performed with the standard plaquette gauge and the $O(a)$-improved Wilson fermion actions on 192$^3 \times N_\tau$ lattices with $N_\tau$ = 96--32, which corresponds to temperatures from 0.73$T_c$ to 2.2$T_c$. To reconstruct the charmonium spectral functions for the Euclidean time correlators we apply two different stochastic methods called Stochastic Analytical Inference (SAI) and Stochastic Optimization Method (SOM), where the former is based on the Bayes' theorem similar to commonly used Maximum Entropy Method (MEM) while the latter does not rely on any prior information. We carefully estimate systematic uncertainties by comparing results among SAI, SOM and also MEM. With the given spectral functions we discuss melting temperatures of charmonia as well as the heavy quark diffusion coefficient.

Speaker: Dr Hiroshi Ohno (University of Tsukuba)

Slides lattice2016_Ohno.pdf

276 A gauge invariant Debye mass for the complex heavy-quark potential

The concept of a screening mass is a powerful tool to simplify the intricate physics of in-medium test charges surrounded by light charge carriers. While it has been successfully used to describe electromagnetic properties, its definition and computation in QCD is plagued by questions of gauge invariance and the presence of non-perturbative contributions from the magnetic sector. Here we present a recent alternative definition [1] of a gauge invariant Debye mass parameter following closely the original idea of Debye and Hueckel. Our test charges are a static heavy quark-antiquark pair whose complex potential and its in-medium modification can be extracted using lattice QCD [2]. By combining in a generalized Gauss-Law the non-perturbative aspects of quark binding with a perturbative ansatz for the medium effects, we succeed to describe the lattice values of Re[V] and Im[V] [3] with a single temperature dependent parameter, in turn identified with a Debye mass. We find that its behavior evaluated both in quenched QCD [4], as well as dynamical Nf=2+1 QCD [3] deviates from that in other approaches, such as hard-thermal-loop perturbation theory or from electric field correlators on the lattice. Around the phase transition e.g. its values tend to zero significantly faster than at weak-coupling. [1] Y. Burnier, A.R. Phys.Lett. B753 (2016) 232-236
[2] A.R., T. Hatsuda, S. Sasaki, Phys.Rev.Lett. 108 (2012) 162001
[3] Y.Burnier, O. Kaczmarek, A.R. Phys.Rev.Lett. 114 (2015) 082001
[4] Y.Burnier, A.R. in preparation

Speaker: Dr Alexander Rothkopf (Institute for Theoretical Physics, Heidelberg University)

Slides LATTICE_ROTHKOPF_FINAL_WEB.pdf

277 Static and non-static vector screening masses

Thermal screening masses associated to the conserved vector current are calculated both in a weak-coupling and a lattice QCD approach. The inverse of a screening mass can be understood as the length scale over which an external electric field is screened in a QCD medium. The comparison of screening masses in the zero and non-zero Matsubara frequency sectors shows good agreement of the perturbative and the lattice results. Moreover, at *T* ≈ 508MeV the lightest screening mass lies above the free result $(2n\pi T)$, in agreement with the $\mathcal{O}(g^2)$ weak-coupling prediction, whereas this was not the case in a previous study at *T* ≈ 254MeV.

Speaker: Mr Aman Steinberg (Uni Mainz)

Slides talk_lat_2016_steinberg.pdf

Physics Beyond the Standard Model

Convener: Prof. Maarten Golterman (San Francisco State University)

278 Phenomenology of a composite Higgs model: lessons for the lattice.

We study the phenomenology of a specific model of strongly interacting dynamics beyond the Standard Model, and derive the current bounds on the low-energy constants that describe the large-distance behaviour of the model. We deduce from these bounds the required accuracy for lattice simulations to have an impact on searches for new physics beyond the Standard Model.

Speaker: Prof. Luigi Del Debbio (Edinburgh)

Slides lat16.pdf

279 Check of a new non-perturbative mechanism for elementary fermion mass generation

We consider a field theoretical model where a SU(2) doublet fermion, subjected to non-abelian gauge interactions, is also coupled to a complex scalar field doublet via a Yukawa and an irrelevant Wilson-like term. Despite the presence of these two chiral breaking operators in the Lagrangian, an exact symmetry acting on fermions and scalars prevents perturbative mass corrections. In the phase where fermions are massless (Wigner phase) the Yukawa coupling can be tuned to a critical value at which chiral transformations acting on fermions only become a symmetry of the theory (up to cutoff effects). In the Nambu-Goldstone phase of the critical theory a fermion mass term of dynamical origin is expected to arise in the Ward identities of the purely fermionic chiral transformations. Such a non-perturbative mechanism of dynamical mass generation can provide a “natural" (a` la 't Hooft) alternative to the Higgs mechanism adopted in the Standard Model.

Speaker: Mr Marco Garofalo (University of Edinburgh)

Slides lattice_2016_GM.pdf

280 Lines of Constant Physics in a 5-d Gauge-Higgs Unification Scenario

We report on the progress in the study of a five-dimensional SU(2) Gauge-Higgs Unification model. In the non-perturbative study, the Higgs mechanism is triggered by the spontaneous breaking of a global symmetry. In the same region of the phase diagram, we observe both dimensional reduction and the ratio of Higgs and Z boson masses to take the value known from experiment. We present the first results on the construction of a line of constant physics in this region, including the prediction for the mass scale of the first excited states of the Higgs and gauge bosons.

Speaker: Mr Maurizio Alberti (University of Wuppertal)

Slides GHU_lattice_2016.pdf

281 Physical spectra and the limits of perturbative estimates in a theory with a Higgs

The spectacular success of perturbation theory in electroweak physics hinges on the validity of the Froehlich-Morchio-Strocchi mechanism. This mechanism allows the determination of the spectrum of physical, gauge-invariant states using perturbation theory if a Brout-Englert-Higgs effect is present. For this mechanism to work two preconditions have to be met. One is the structural requirement that the perturbative multiplet structure can be mapped to the physical one. The other requires that dynamically the pole structure of gauge-dependent correlation functions is not qualitatively altered. To assess the validity of perturbation theory to describe the spectrum in beyond-the-standard model calculations requires to understand when these conditions are fulfilled. The second condition will be investigated in the Yang-Mills-Higgs case on the lattice. It is found that it depends crucially on the parameters whether this condition is fulfilled. Even in cases where perturbation theory should be expected to work well it turns out that it does not. Various possibilities for a criterion for this breakdown will be discussed. As a side-effect the physical spectrum of the theory in a wide range of the phase diagram is uncovered, which is also valuable for several other research directions.

Speaker: Prof. Axel Maas (University of Graz)

Slides lattice16.pdf

282 The physical spectrum of a partially Higgsed gauge theory

The description of electroweak physics using perturbation theory is highly successful. Though not obvious, this is due to a subtle field-theoretical effect, the Fröhlich-Morchio-Strocchi mechanism, which links the physical spectrum to that of the elementary particles. This works because of the special structure of the standard model, and it is not a priori clear whether it works for structurally different theories. Candidates for conflicts are, e.g., partially Higgsed gauge theories. We study this situation in an $SU(3)$ gauge theory with one fundamental Higgs field and a breaking pattern $SU(3) \rightarrow SU(2)$. We determine the leading order predictions for the gauge invariant spectrum in this theory and discuss the results from lattice simulations.

Speaker: Mr Pascal Toerek (University of Graz)

Slides lattice16_toerek.pdf

Weak Decays and Matrix Elements