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Dr
Wolfgang Bietenholz
(UNAM, Mexico)
25/07/2016, 14:15
Theoretical Developments
Talk
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....
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Dr
Julien Frison
(KEK Theory Center)
25/07/2016, 14:35
Theoretical Developments
Talk
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...
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Prof.
Shailesh Chandrasekharan
(Duke University)
25/07/2016, 14:55
Theoretical Developments
Talk
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...
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Dr
Simon Mages
(Forschungszentrum Jülich)
25/07/2016, 15:15
Theoretical Developments
Talk
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...
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Dr
Balint Toth
(Bergische Universität Wuppertal)
25/07/2016, 15:35
Theoretical Developments
Talk
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...
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Arata Yamamoto
(University of Tokyo)
25/07/2016, 15:55
Theoretical Developments
Talk
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.
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Jacek Wosiek
(Jagellonian University)
25/07/2016, 16:45
Theoretical Developments
Talk
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...
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Mr
Hikaru Kawauchi
(Kanazawa University)
25/07/2016, 17:05
Theoretical Developments
Talk
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.
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Stefan Kühn
(Max Planck Institute of Quantum Optics)
25/07/2016, 17:25
Theoretical Developments
Talk
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...
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Dr
Pavel Buividovich
(Regensburg University)
25/07/2016, 17:45
Theoretical Developments
Talk
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...
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Dr
Tobias Hartung
(King's College London)
25/07/2016, 18:05
Theoretical Developments
Talk
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...
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Masanori Hanada
(Kyoto U, Stanford U)
25/07/2016, 18:25
Theoretical Developments
Talk
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,...
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Dr
Akaki Rusetski
(HISKP, University of Bonn, Germany)
26/07/2016, 14:00
Theoretical Developments
Talk
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...
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Dr
Maxim Mai
(George Washington University)
26/07/2016, 14:20
Theoretical Developments
Talk
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...
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Mr
Daniel Robaina
(Institute for Nuclear Physics Mainz)
26/07/2016, 14:40
Theoretical Developments
Talk
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...
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Ms
Julia Volmer
(DESY Zeuthen)
26/07/2016, 15:00
Theoretical Developments
Talk
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...
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Prof.
Ulli Wolff
(HU Berlin)
26/07/2016, 15:20
Theoretical Developments
Talk
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...
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Prof.
Yannick Meurice
(University of Iowa)
26/07/2016, 15:40
Theoretical Developments
Talk
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...
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Dr
Hidenori Fukaya
(Osaka University)
26/07/2016, 16:30
Theoretical Developments
Talk
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...
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Mr
Ryo Yamamura
(Osaka U.)
26/07/2016, 16:50
Theoretical Developments
Talk
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...
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Mr
Jishnu Goswami
(IIT Kanpur)
26/07/2016, 17:10
Theoretical Developments
Talk
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...
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Prof.
Roberto Frezzotti
(University of Rome Tor Vergata, Physics Department and INFN - Sezione di Roma Tor Vergata)
26/07/2016, 17:30
Theoretical Developments
Talk
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...
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Venkitesh Ayyar
(Duke University)
26/07/2016, 17:50
Theoretical Developments
Talk
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...
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Mr
Ryo Sakai
(Kanazawa University)
26/07/2016, 18:10
Theoretical Developments
Talk
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...
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Susanne Ehret
(University of Edinburgh)
27/07/2016, 09:00
Theoretical Developments
Talk
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...
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Mr
Francesco Capponi
(Plymouth University)
27/07/2016, 09:20
Theoretical Developments
Talk
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...
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Dr
Mattia Dalla Brida
(DESY - Zeuthen)
27/07/2016, 09:40
Theoretical Developments
Talk
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...
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Ms
Dorota Grabowska
(INT/UW)
27/07/2016, 10:00
Theoretical Developments
Talk
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...
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Prof.
Richard Richard Brower
(Boston University)
27/07/2016, 10:20
Theoretical Developments
Talk
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...
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Prof.
Margarita Garcia-Perez
(Instituto de Fisica Teorica UAM-CSIC)
27/07/2016, 11:30
Theoretical Developments
Talk
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...
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Prof.
Masanori Okawa
(Hiroshima University)
27/07/2016, 11:50
Theoretical Developments
Talk
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.
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Prof.
Antonio Gonzalez-Arroyo
(Instituto de Fisica Teorica UAM/CSIC)
27/07/2016, 12:10
Theoretical Developments
Talk
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.
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