YTF 9

11 Jan 2017, 12:00 → 12 Jan 2017, 14:30 Europe/London

James Whitehead (IPPP, Durham)

Welcome to YTF 9 taking place at Durham University on the 11th and 12th of January 2017. The purpose of YTF is to bring together postgraduate students working in theoretical physics, providing the opportunity to present their work to a sympathetic audience. We hope to foster development of early career researchers and encourage collaboration between different universities.

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Topics to be discussed include:

• Beyond Standard Model Physics
• String Phenomenology
• Holography
• Cosmology
• Amplitudes
• Solitons
• Standard Model Phenomenology
• String Theory
• QCD
• Gravity

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Abstract submission will open on the 1st of November.

For more information, please visit our website and follow our Twitter account to stay up to date on the latest news.

Wednesday, 11 January

12:30 → 13:30 Lunch

13:30 → 14:30 Registration

Registration for YTF9

14:00 → 14:30 Check-in at accommodation

Check in at the accommodation for YTF9

14:30 → 14:35 Welcome

Convener: Mr Sam Fearn (Durham University)

14:35 → 16:15 Parallel Sesion: BSM Theory and Lattice

Convener: Mr Andres Olivares del Campo (IPPP, Durham University)

14:35 Non-Standard Mechanisms for Neutrinoless Double Beta Decay, Their Probes and Implications

In my talk I will describe the effective approach to lepton number violation and implications of potential future observation of lepton number violating (LNV) processes, primarily of neutrinoless double beta decay. The interplay between lepton number violation at high and low energies is of particular interest, as the constraints on theories of baryogenesis can be obtained. One can state that if neutrinoless double beta decay is trigerred by other than the standard mass mechanism, then the usual high-scale baryogenesis models will be excluded. As can be shown, each LNV effective operator contributes to neutrinoless double beta decay in a number of ways and the understanding of the mutual relations among all the operators is crucial when determining the dominant contribution. Moreover, the nuclear side of the problem plays an important role, as a thorough calculation of corresponding nuclear matrix elements is needed for the estimation of the effective couplings and it can also help to pinpoint the dominant mechanism triggering neutrinoless double beta decay. Apart from the effective field approach, I will also outline the possible extension of our arguments to a general UV-completed model.

Speaker: Lukas Graf (University College London)

Slides graf_YTF_9.pdf

15:00 Creating the Baryon Asymmetry from Lepto-Bubbles

We propose a new mechanism to generate a lepton asymmetry based on the vacuum CP-violating phase transition (CPPT). This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This mechanism provides strong connections with low-energy neutrino experiments.

Speaker: Ms Jessica Turner (IPPP, Durham University)

Slides YTF2017.pdf

15:25 Effective Potentials and Radiative Mass Generation

The talk shall focus around explaining the role of effective potentials in theories that incorporate spontaneous symmetry breaking and how they contribute in radiative mass generation, along with their implementation in different models.

Speaker: Mr Dumitru Dan Smaranda (University of Glasgow)

Slides main.pdf

15:50 A lattice probe of flavour physics: the Bs to Ds decay

There is something afoot in flavour physics. A number of related anomalies concerning B decays, which are intimately linked to CKM matrix elements, have surfaced over the years. I will give an overview of an ongoing calculation of the Bs to Ds decay using lattice QCD, which may shed some light on what new thing could be lurking in the flavour sector.

Speaker: Mr Euan McLean (Glasgow University)

Slides YTF9.pdf

15:00 → 16:15 Parallel Sesion: String Theory

Convener: Mr Vaios Ziogas (Durham University)

15:00 Model-building in heterotic string theory

Model-building in string theory explores the question of producing at low-energies the Standard Model of particle physics from an underlying string theory. Heterotic $E_8 \times E_8$ string theory is one prominent avenue for model-building. Recently it has become possible to scan over large regions of the space of possible models, resulting in very many phenomenologically interesting models with the correct gauge group and matter content of the Standard Model. I will discuss work in this area, in particular in the context of heterotic/F-theory duality.

Speaker: Mr Callum Brodie (University of Oxford)

Slides callum_brodie_talk.pdf

15:25 Moonshine: Unexpected symmetries in string theory

Mathieu Moonshine concerns a surprising observation relating string theory to the representation theory of a particular sporadic group, Mathieu 24. This is reminiscent of Monstrous Moonshine in which it was discovered that the coefficients of the modular j-function are related to the representation theory of the Monster group. In this talk we will briefly review the Monstrous and Mathieu moonshines, before discussing objects analagous to those appearing in these stories in a new class of theories.

Speaker: Mr Sam Fearn (Durham University)

Slides YTF_Talk.pdf

15:50 M-Branes and Gauge Theories

In this talk I will give a review of developments over the past few years in the study of Brane dynamics in M- theory. I will begin with a brief discussion of what M- theory is, and what Branes it contains. I will then examine the various attempts to use gauge theories to probe the low energy dynamics of M2 branes, analogous to the use of SU(N) Super Yang Mills to describe interacting D Branes in String theory. I will conclude by outlining the much more challenging problem of interacting M5 Branes- the (2,0) theory

Speaker: Mr Calum Robson (Durham University)

Slides YTFtalk.pdf

16:15 → 16:40 Tea and Coffee

16:40 → 17:55 Paralell Session: Neutrinos

Convener: Mr Kristian Moffat (IPPP)

16:40 The Nu Kid on the Block: Sterile Neutrinos at the eV Scale

In this talk we will briefly review our understanding of neutrino oscillations and discuss some of the anomalies at short baseline experiments. These anomalies point towards the existence of a sterile neutrino with a mass at the eV scale and have been the motivation behind many of the efforts in the neutrino community. Some of the motivations and implications of such a sterile are discussed. We will then present our most recent work on NuSTORM, an experimental proposal that looks to search for such steriles in a novel way.

Speaker: Mr Matheus Hostert (Durham University)

Slides HostertMTalk

17:05 Precision neutrino experiments versus the Littlest Seesaw

We present a study into the extent that upcoming precision neutrino oscillation experiments will exclude one of the most predictive models of neutrino mass and mixing: the Littlest Seesaw. This model provides a good fit to current data, predicting eight observables from two input parameters, and provide new assessments of its predictions and their correlations. The ability to exclude this model is assessed using simulations of upcoming neutrino oscillation experiments including the medium-distance reactor experiments JUNO and RENO-50 and the long-baseline accelerator experiments DUNE and T2HK. We show that an accurate determination of the currently least well measured parameters, namely the atmospheric and solar angles and the CP phase $\delta$, provide crucial independent tests of the model. For $\theta_{13}$ and the two mass-squared differences, however, the model's exclusion requires a combination of measurements coming from a varied experimental programme. These results show that the synergy and complementarity of future experiments will play a vital role in efficiently discriminating between predictive models of neutrino flavour, and hence, towards advancing our understanding of neutrino oscillations in the context of the flavour puzzle of the Standard Model.

Speaker: Mr Nick Prouse (Southampton & Queen Mary University of London)

Slides YTF2017.pdf

17:30 Reducing the solar neutrino background in dark matter searches using polarized helium-3

Future dark matter detectors plan to have sensitivities such that solar neutrinos will start to become a problematic background. In this work, we show that a polarized helium-3 detector would, in principle, be able to eliminate 98% of these events when the orientation of the polarization axis is antiparallel to the direction of the Sun. We comment on the possible improvement in sensitivity of dark matter direct detection experiments due to this effect and the feasibility of building such a detector.

Speaker: Mr Tarso Franarin (King's College London)

16:40 → 17:55 Parallel Session: Holography

Convener: Maciej Matuszewski (Durham University)

16:40 A first law for entanglement rates

The first law of entanglement entropy states that under a perturbation of the state of a CFT, the change in entanglement entropy is proportional to the change in energy. We use holography to study entanglement entropy in conformal field theories perturbed by a source linear in time. Under certain assumptions, we find that the first law may be violated, however the rates of change of the entanglement entropy and energy are proportional. An explicit example is presented for CFTs deformed by marginal scalar operators.

Speaker: Mr Ronald Rodgers (University of Southampton)

Slides first_law_rates.pdf

17:05 Thermal Conductivity on Curved Manifolds in the Hydrodynamic Limit

In this talk we are going to study hydrodynamics on curved manifolds, inspired by the holographic prescription for obtaining the thermoelectric DC conductivities of the boundary theory by solving the Navier-Stokes equations on black hole horizons. We place the underlying conformal field theory on curved space and we derive the Navier-Stokes equations after the application of a thermal gradient. We also discuss aspects of the thermal DC and AC conductivities in the hydrodynamic limit.

Speaker: Mr Vaios Ziogas (Durham University)

Slides Vaios_Ziogas_YTF9_talk_v2.pdf

17:30 Resurgence and Hydrodynamics in Gauss Bonet Holography

Due to a correspondence between Hydrodynamics and Gravity, one can study a fluid-like Quark-Gluon Plasma (QGP) at infinite coupling through perturbations of a boosted blackbrane solution in General Relativity. In previous work the late time expansion of Bjorken flow (1-dimensional, boost-invariant flow as present during Heavy Ion collisions) was computed in a gradient expansion to high orders and the technique of Resurgence was used to understand the emergence of non-hydrodynamic modes in the structure of large order perturbation. As a first step towards understanding finite coupling corrections to the non-hydrodynamic behavior of the QGP, we will extend this method in Gauss-Bonnet Gravity, a higher derivative extension of Einstein gravity.

Speaker: Mr Ben Meiring (University of Oxford)

Slides meiring_ytf_2017.pdf

17:55 → 18:15 Tea and Coffee

18:15 → 19:15 Physics in 2017: Something's funny?: Talk by Dr. Donal O'Connell

Convener: Mr Andres Olivares del Campo (IPPP, Durham University)

19:15 → 20:30 Poster and Pizza

Thursday, 12 January

09:00 → 10:40 Parallel Sesion: BSM Phenomenology

Convener: Mr Philip Waite (IPPP, Durham)

09:00 Supersymmetric decays in Softsusy

I will discuss the addition of a decay calculator to the SoftSusy spectrum generator program currently used for susy searches. The new version of softsusy -4.0 will therefore now be able to provide all-in-one spectrum generation and decay calculation including all tree-level Susy 1 → 2 decays, relevant 1 → 3 decays, all relevant higgs decays including Zgamma, gamma gamma, glu glu, and crucially, all NMSSM 1 → 2 decays. The motivations and benefits for adding such decays to the program will be explained, along with how the program works, how to use it and some interesting scenarios the program can help examine.

Speaker: Mr Thomas Cridge (DAMTP, University of Cambridge)

Slides Durham_YTF_Seminar_Thomas_Cridge.pdf

09:25 Soft physics and interpretation challenges for LHC supersymmetry searches

As supersymmetry searches confront the LHC energy ceiling, what will shape future searches given the dearth of signals? Discovery opportunity remains in the colourless sector, where lower mass bounds are around 100 GeV for scalar leptons and fermionic Higgs particles. High luminosity will probe their rare production and I will discuss overcoming experimental challenges to detect the low energy 'soft' decay products. Further, how should the rich programme of LHC searches leave an impactful legacy? I will explore theoretical frameworks being developed to interpret experimental results beyond simplified models, be it to characterise new signals or constrain realistic supersymmetry scenarios.

Speaker: Jesse Liu (Oxford University)

Slides JesseLiu_YTF9.pdf

09:50 Hunting for Minimal Walking Technicolor using Z’/Z’’ searches at the LHC

Despite the successes of the Standard Model, there are many issues and open questions that must be answered with physics Beyond the SM. For 4 decades, theories of strong dynamics, in particular Technicolor theory, have been posed as alternatives to spontaneous electroweak symmetry breaking. Today, Walking Technicolor theory offers both a solution to the hierarchy problem, a Higgs boson-like particle corresponding to observation, and a rich phenomenology which we can explore within the current energy capabilities of the LHC. We explore signals of new neutral resonances in WTC at the LHC, to give the strongest constraints on WTC to date, and possibly to determine the future of Technicolor theory and strong dynamics.

Speaker: Ms Azaria Coupe (Univeristy of Southampton)

Slides azaria_coupe_ytf_talk.pdf

10:15 Dijets and Dark Matter

Searches for Dark Matter (DM) at the LHC using effective field theory can be unreliable as we cannot guarantee the cut-off in such theories is above the typical energy involved in a LHC collision. Therefore a set of simplified models are typically used to interpret LHC data, with a dynamical mediator present in the model that is responsible for the interactions between the dark and visible sectors. Direct searches for such mediators then complement more traditional missing energy signatures of DM. Dijets are a good example of this and I will present a recasting of dijet data in terms of a spin-one mediator coupling to quarks (a leptophobic Z') in a reasonably general and model independent way. I will then show a novel way of combining these bounds with the requirement that the theory accounts for all the DM in the universe today.

Speaker: Mr Patrick Tunney (King's College London)

Slides YTF_talk_2017.pdf

09:00 → 10:40 Parallel Sesion: Gravity and Gauge Theories

Convener: Mr Calum Robson (Durham University)

09:00 Black Holes and the Double Copy

The "double copy" expresses gravity as the square of Yang-Mills. This elegant property was originally found for amplitudes, since it has been proven to tree level it must also be true for classical theory as well. Excitingly, this means that black holes and other exact solutions to general relativity can be described without needing perturbation theory. This talk will explore the relationship between general relativity and Yang-Mills theory in more depth and will detail recent progress in "double copying" black holes.

Speaker: Isobel Nicholson (University of Edinburgh)

09:25 Asymptotic safety and fixed points of gauge theories

Ultraviolet fixed points of the renormalisation group flow allow one to define quantum field theories which are valid up to arbitrarily high energies. However, finding fixed points is a difficult problem in general as one has an infinite number of couplings to deal with. In this talk I will discuss how restricting to the case of weakly coupled four-dimensional gauge theories allows for a complete classification of the types of fixed points which are possible, and the role Yukawa couplings play in offering a unique mechanism to allow such non-trivial fixed points to be ultraviolet.

Speaker: Mr Andrew Bond (University of Sussex)

Slides YTF-Jan-17.pdf

09:50 Does my favourite QFT have a standard UV completion?

Many quantum field theories are only well-defined at low energies - with a breakdown of unitarity above some energy cutoff. If there is a physically sensible way to introduce new degrees of freedom which restore unitarity, then this apparent breakdown needn't worry us - we say that the original theory admits a *UV completion*. However, if it is **not** possible to UV complete the theory, this is very troublesome - it means that the original low energy theory cannot describe a reality which is consistent with QFT's axioms (i.e. our Universe). So it is of great importance to establish whether our favourite QFTs (whatever they may be) can have UV completions. In this talk I will present some conditions which any low energy effective field theory ought to satisfy in order to have a standard UV completion, and discuss the particular example of massive gravity.

Speaker: Mr Scott Melville (Imperial College London)

Slides Melville_YTF9_12Jan2017_SingleSlide.pdf

10:15 A Geometric Approach to Scattering Amplitudes in $\mathcal{N} = 8$ Supergravity

I will introduce the language of on-shell diagrams for calculating scattering amplitudes via BCFW recursion in $\mathcal{N} = 4$ super Yang Mills theory, and then explain how they can be extended to $\mathcal{N} = 8$ supergravity. I will describe how this approach relates scattering amplitudes to the Grassmannian Gr$(k,n)$, a purely geometric object describing the space of $k$ planes in $n$ dimensions. This link to the Grassmannian exposes a duality between on-shell diagrams and ambi-twistor string theory, and I will present my work in progress in this area.

Speaker: Mr Joseph Farrow (Durham University)

10:40 → 11:00 Tea and Coffee

11:00 → 13:05 Parallel Sesion: Dark Matter

Convener: Mr Tarso Franarin (King's College London)

11:00 Distinguishing Dark Matter in Direct Detection

A new generation of Direct Detection Experiments are now running, and with an ever increasing number of Dark Matter particle models, it is important to interpret new data agnostically. The Non-Relativistic Effective Field Theory approach is particularly well suited to this task, and encapsulates behaviour of elastic scattering in DD Experiments in a very general way. In this talk I will look at recent efforts to distinguish just how much information about the particle nature of DM we can glean from DD experiments.

Speaker: Mr Andrew Cheek (Institute of Particle Physics Phenomenology)

Slides YTF_talk.pdf

11:25 Direct WIMP searches with the LUX-ZEPLIN experiment

One of the major challenges of modern physics is to discover the nature of dark matter, an invisible and dominant mass component of the observable universe that is indirectly revealed through its gravitational effects on ordinary matter. Assuming that dark matter is made of new elementary particles, a well-motivated and generic class of dark matter candidates are weakly interacting massive particles (WIMPs), which arise naturally in several extensions to the Standard Model. WIMPs could be directly detected via their scattering off atomic nuclei in underground, ultra low-background detectors. In this report, an overview of the dark matter direct detection LZ experiment is given, which originates from the merging of the successful ZEPLIN experiments in the UK and LUX experiment in the US. With its 7 tonnes of active liquid xenon, it is expected that the LZ experiment will probe WIMP interactions practically as far as it is allowed by new backgrounds from astrophysical neutrinos.

Speaker: Mr Ibles Olcina (United Kingdom: Imperial College London, South Kensington campus)

Slides YTF2017_IO.pdf

11:50 Simulating Massive Halos to Constrain the Nature of Dark Matter

Observations of strong gravitational lenses offer a powerful new method to distinguish the cold dark matter paradigm from other models such as warm or self-interacting dark matter. In this talk I will outline this method, and discuss how predictions for observations are calculated.

Speaker: Mr Jack Richings (Durham University)

Slides ytf9_talk.pdf

12:15 The 3.5 keV line in Perseus: Evidence for Fluorescent Dark Matter

An excess of X-Rays at 3.5 keV detected in various galaxies and clusters, including the Perseus cluster, has generated a lot of excitement as a potential Dark Matter signal. Hitomi observations of Perseus with the Soft X-ray Spectrometer (SXS) provide a high-resolution look at the 3.5 keV feature. The Hitomi spectrum -- which involves the sum of diffuse cluster emission and the point-like central Active Galactic Nucleus (AGN) -- does not show any excess at E ~ 3.5keV, giving an apparent inconsistency with previous observations of excess diffuse emission. We point out that 2009 Chandra data reveals a strong dip in the AGN spectrum at E = (3.54 ± 0.02) keV (cluster frame) -- the identical energy to the diffuse excess observed by XMM-Newton. Scaling this dip to the 2016 AGN luminosity and adding it to the diffuse XMM-Newton excess, this predicts an overall dip in the SXS field of view of (-7.7 ± 4.6) x 10-6 ph cm^-2 s^-1 at E = 3.54 keV, a precise match to the Hitomi data when broadened by the dark matter virial velocity. We describe models of Fluorescent Dark Matter that can reproduce this physics, in which dark matter absorbs and then re-emits 3.5 keV photons emitted from the central AGN.

Speaker: Mr Nicholas Jennings (University of Oxford)

Slides YTFTalkJennings.pdf

12:40 The Sun as a Laboratory for Electromagnetic Dipole Dark Matter

In recent years, a revised set of solar abundances has led to a discrepancy in the sound-speed profile between helioseismology and theoretical solar models. Conventional solutions require additional mechanisms for energy transport within the Sun. Vincent et al. have recently suggested that dark matter with a momentum or velocity dependent cross section could provide a solution. In this work, we consider three models of dark matter with such cross sections and their effect on the stellar structure. In particular, the three models incorporate dark matter particles interacting through an electromagnetic dipole moment: an electric dipole, a magnetic dipole or an anapole. Each model is implemented in the DarkStec stellar evolution program, which incorporates the effects of dark matter capture and heat transport within the solar interior. We show that dark matter with a mass of 3 GeV and an electric dipole moment or an anapole moment of may possibly improve the sound-speed profile, small frequency separations and convective zone radius with respect to the Standard Solar Model. However, the required dipole moments are strongly excluded by direct detection experiments.

Speaker: Mr Ben Geytenbeek (University of Cambridge)

Slides ytf9presentation.pdf ytf9presentationshort.pdf

11:00 → 13:05 Parallel Sesion: Gravity and Cosmology

Convener: Ms Jessica Turner (IPPP, Durham University)

11:00 Disformally self-tuning gravity

We extend a previous self-tuning analysis of the most general scalar-tensor theory of gravity in four dimensions with second order field equations by considering a generalized coupling to the matter sector. Through allowing a disformal coupling to matter we are able to extend the Fab Four model and construct a new class of theories that are able to tune away the cosmological constant on Friedmann-Lemaitre-Robertson-Walker backgrounds.

Speaker: Mr William Emond (University of Nottingham)

Slides YTF_2017_self-tuning_gravity_talk.pdf

11:25 Khronometric Theory, Numerical General Relativity and Blackholes

In Khronometric theory we break Lorentz invariance by introducing a preferred time direction, and hence, equipping our spacetime manifold with a foliation of space-like surfaces. Our primary tool to solve the equations of motion is such a spacetime is Numerical General Relativity (NGR). We investigate how we can use this tool, to solve the equations of motion for a blackhole solution in Khronometric Theory.

Speaker: Mr James Cook (King's College London)

Slides Khronometric_Theory_James_Cook.pdf

11:50 Black hole formation from axion stars

The classical equations of motion for an axion possess localized, oscillating solutions, which we refer to as "axion stars". We study, for the first time, collapse of axion stars numerically using the full Einstein equations of general relativity. We identify three states: i) long-lived oscillating axion star solutions ii) collapse to a BH and iii) complete dispersal due to gravitational cooling and interactions.

Speaker: Mr Thomas Helfer (Kings College London)

12:15 Gravitational particle production after Reheating

Due to change of space-time during Inflation and Reheating, spectators field present during these epochs are going to be excited. This can be seen as a particle production. I am going to present the production of a field with no coupling to any other field, the only possible way of interaction will be through gravity. Some problems will arise due to the divergences present in this model and I will show how to deal with them and how to obtain the abundance of this particle today. If this is the method to produce the dark matter abundance today, some bounds can be imposed on the mass of Dark matter and the energy scale of Inflation and Reheating.

Speaker: Mr David Rodriguez Roman (King's College London)

Slides YTF_DavidRodriguez.pdf

12:40 Discussion

13:05 → 14:30 Lunch