Applications of gauge/gravity duality

• Matthew Russell (Southampton)

Room: CM107 This talk will discuss scenarios where the gauge/gravity duality can be applied to non-perturbative regimes in physics. The standard model explains many phenomena seen in nature but relies on techniques that only work in small coupling. The gauge/gravity duality is a way in which we can try to obtain theoretical predictions for areas such as strongly coupled condensed matter and the low energy regime of QCD. Specifically this talk will focus on momentum dissipation effects on zero sound in strange metals and the benefit of exploring holographic imaginary chemical potential in the QCD phase diagram.

Coincident M5-branes and dual singular geometries

• Callum Brodie (University of Oxford)

Room: CM107 Through a web of string dualities, M5-brane configurations in M-theory can be mapped to geometrical features. In particular, I will discuss this map via heterotic/F-theory duality, using a Horava-Witten description of heterotic $\mathrm{E}_8 \times \mathrm{E}_8$ string theory as the connection to M-theory. Intersecting or coincident M5-branes are mapped to singular base geometries in F-theory, which also correspond to singular geometries in Type IIB string theory. I will explain these dualities, and if I have time I will discuss geometrical transitions corresponding to deforming M5-brane configurations and point out some cute connections with toric geometry.

Central charge of self-dual strings from holography

• Ronnie Rodgers (University of Southampton)

Room: CM107 M-theory is a candidate for a theory of quantum gravity. Its fundamental objects are called M2-branes and M5-branes. The low-energy theory describing coincident M5-branes is poorly understood in many respects, with holography providing one of the most useful tools to further that understanding. It is known that the theory should possess solitonic solutions called "self-dual strings". I will review the holographic description of these strings, and show how calculation of entanglement entropy provides a way of calculating an important quantity characterising them: their central charge.

Anisotropies in the stochastic gravitational-wave background

• Alex Jenkins (King's College London)

Room: CM101 In the new era of gravitational-wave astronomy, one of the most exciting targets for future observations is the stochastic gravitational-wave background (SGWB). While we have yet to detect the SGWB, we expect that by studying the angular power spectrum of its anisotropies, we may learn about the large-scale structure of the Universe (analogous to studies of the CMB). With this in mind, we develop detailed models of the SGWB anisotropies from two important sources of gravitational waves: unresolved compact binary coalescences, and cosmic strings.

Bifurcations in the RG-Flow of QCD

• Folkert Kuipers

Room: CM101 In this talk, I’ll discuss the connection between the theory of dynamical systems and renormalization group flows in quantum field theory. In particular, I’ll apply numerical methods from bifurcation analysis to study the RG-flow of an effective model for QCD with a four-fermi interaction and an arbitrary number of colors and massless flavors. Using bifurcation analysis techniques, new fixed points are found in and close to the conformal window. Particular focus will be given to the way in which the fixed points (dis)appear in the model, and how this affects the scaling dimensions of the (ir)relevant operators. Furthermore, I’ll discuss how the fixed point structure of the RG-flow changes when a scalar field coupling through a Yukawa interaction is added to the model.

Global Fixed Points of Scalar and Fermionic Theories

• Bradley Garland (University of Sussex)

Room: CM101 Interacting fixed points in three dimensions have been investigated using modern renormalisation group methods. Investigations focus on the seminal Wilson-Fisher fixed point solution in O(N) symmetric scalar theories and asymptotically safe UV fixed points in fermionic Gross-Neveu models. The main novelty of the study is the use of Padé approximants. Padé approximants have been used to extend local fixed point data that is obtained from polynomial expansions and hence, only valid for small field values to global fixed point solutions for all field values. For both the scalar and fermionic theories this approach is tested in the Large N limit where explicit analytic fixed point solutions can be found. Particular emphasis is put on the large real field and the large imaginary field limits, and converging-limiting singularities in the complex field plane. Finite N models have also been tested for the O(N) symmetric scalar theories. Here exact solutions are not accessible and Padé approximants have been used to make predictions beyond the radius of convergence of polynomial expansions. Padé approximants have also been used to locate singularities exhibited by the given complexified fixed point solutions. In doing this it is seen that the singularities exhibited by Padé approximants themselves form patterns of defects in the complexified field plane that are intimately linked to their ability to converge to high accuracy.

Renormalization Group Properties of the Conformal Mode

• Matthew Kellett (University of Southampton)

Room: CM101 The renormalization group properties of a QFT are of profound importance to the theory. In quantum gravity, one runs into the problem that the kinetic term for the dilaton (or conformal mode) has the wrong sign, causing the Euclidean partition function to be (worse than usually) ill-defined. Imposing a new quantization condition allows us to not only make sense of this, but also potentially would allow us to use standard RG techniques to quantize gravity. We see that the effect of resolving this conformal mode "instability" (as described by Hawking et. al.) is to constrain the size of the manifold by its homogeneity. I will present an outline of how this is done and some results from studies of the torus. If time permits, I will also outline ongoing and future work in this area.

Clustering algorithms for b-jets from BSM Higgs Bosons.

• Billy Ford (University of Southampton)

Room: CM101 It is long established that the Standard Model is not a complete theory of nature and at the LHC we hope to see hints of some new physics beyond our current understanding. This project seeks to improve current techniques of jet clustering, in particular from some extended BSM Higgs sector, such as those in 2 Higgs Doublet Models, which include additional particles alongside the 125 GeV SM Higgs detected in 2012.

A Gentle Introduction to Supersymmetric Localization

• Matthew Renwick (Department of Mathematical Sciences, Durham University)

Room: CM107 Localization is a powerful technique utilised in supersymmetric field theories to reduce troublesome infinite dimensional path integrals to pleasant finite dimensional integrals. The aim of this talk is to provide an introduction to this topic and discuss its applications. In particular, I will explain how this technique is used to compute the exact partition function and the expectation values for certain operators in supersymmetric theories.

Different aspects of single top quark and DM channel

• Charanjit Kaur Khosa (University of Sussex)

Room: CM101 Recently it has been pointed out that associated production of dark matter with single top quark could also provide an interesting reach for dark matter (DM) searches at LHC. I will discuss this in context of simplified dark matter models and in two Higgs doublet model. The top quark produced via this channel is polarized and the polarization depends on the CP of the mediator (simplified dark matter model with spin-0 mediators). I will also talk about the top polarization sensitive angular observables, which along with the cross-section, could be used to probe the CP property of the mediator.

Non-Minimal Flavour Violation in the MSSM from a flavoured SU(5) GUT

• Sam Rowley (University of Southampton)

Room: CM101 We study flavour-violation in a SU(5) setup inspired by flavoured GUTs. We investigate the impact of various observables at low scales on the high-energy parameters of the theory including mu->e gamma and the relic density of dark matter. An interesting interplay between the quark and lepton sectors becomes apparent due to the cohabitation of various fields in representations of the unifying group. Correlations between high scale parameters in the context of current experimental flavour data are shown to manifest. We show that movement away from the Minimal Flavour Violation paradigm is perfectly possible within the context of current limits.

Gravity amplitudes, observables and classical scattering

• Maybee Ben (University of Edinburgh)

Room: CM107 Modern amplitudes techniques offer the tantalising possibility of greatly simplifying theoretical predictions for precision gravitational wave astronomy. One exciting example is the double copy, an enigmatically simple connection between Yang-Mills theory and gravity. In this talk I will discuss our recent work on rigorously obtaining classical scattering observables from quantum amplitudes, and why the double copy makes this pertinent for gravitational radiation.

Developing an amplitude level parton shower.

• Jack Holguin (The University of Manchester)

Room: CM101 Perturbative QCD suffers from multitudes of large logarithms, arising from the miscancellation of infra-red poles. These logarithms can cause enhancements of high order terms and spoil perturbative convergence. Historically there has been two disjoint approaches to solving this problem; resummations and parton showers. Nowadays resummations are performed at high accuracy and are rigorously defined, but they are very time consuming. Parton showers are all purpose and can be implemented computationally. However modern showers are still far from a rigorous definition. We present a new algorithm that aims to unify these two approaches.

Non-perturbative aspects of Sp(2N) gauge theories.

• Jack Holligan (Swansea University)

Room: CM101 The discovery in 2012 of the Higgs boson provided evidence for our understanding of the origin of mass. However there still remain some unanswered questions one of which is the "Naturalness Problem". Like the other fundamental particles, the Higgs acquires loop corrections to its mass due to its interaction with the quarks, the leptons and itself. If we impose an ultraviolet cutoff, $\Lambda_{\text{UV}}$, on the Standard Model, these corrections depend quadratically on $\Lambda_{\text{UV}}$. If $\Lambda_{\text{UV}}$ is sent to infinity, a very large counter term is required to cancel out the quadratic divergence arising from the loop corrections. In order to produce the small observed Higgs mass of $125$ GeV, the counter term must be computed to a precision so high that it is not only unnatural - hence the name - but far beyond experimental reach. One way to resolve this problem is to treat the Higgs not as a fundamental particle but as a constituent one (like the proton or neutron). The need for fine-tuning is simply an effect of the approximation of the Higgs as a fundamental particle breaking down. The compositeness deals with the issue of fine tuning and the subsequent low mass is achieved by corollary of Goldstone's Theorem. When a symmetry is explicitly broken (e.g. by a mass term) there exists a light boson for each broken generator (as opposed to a massless boson in the case of spontaneous symmetry breaking). The explicit breaking of a new symmetry group could give rise to what is observed as the Higgs boson. The combination of Goldstone's Theorem and a new symmetry group have potential to explain the low-mass Higgs as a composite particle without the need for fine-tuning. Candidate symmetries are the Symplectic Groups (denoted as Sp($2N$)). Observable quantities of such a Quantum Field can be computed on the lattice and their experimental detection would provide evidence for same.

Isospin breaking corrections to leptonic decay rates on the lattice

• James Richings (stfc southampton phd student and former durham undergraduate student)

Room: CM101 Lattice QFT is a method for calculating non-perturbative physics and has been used extensively to calculate properties of low energy QCD. Over the last decade calculation's of a number of non-perturbative QCD quantities have reached a good precision, with agreement from across the lattice community. In general isospin breaking (IB) effects have not been included in these calculations because until now IB effects have not been a limiting source of systematic error. Isospin breaking effects enter in two ways, the difference in the mass of the up and down quark (strong IB) and the difference in the QED charge of up and down type quarks (QED IB). Considering power counting these effects are expected to be of the order 1% of the decay rate. Due to the introduction of QED effects, we must calculate the full QCD + QED path integral on the lattice and this introduces a number of complications. In this presentation, I will introduce Lattice QCD+QED as a calculation method for flavour physics observables and discuss how leptonic decay rates are calculated on the lattice with the inclusion of isospin breaking effects.