Student Speaker Abstracts

Formal theory

Jamie Rogers

Liverpool University

String phenomenology and quartic fermionic terms on branes.

I will give an introduction to some of the current efforts to obtain a small, positive cosmological constant from string theory, and the conjectures that may well crush these hopes. Then I will look at the role that high-order fermionic couplings could play and discuss details of the calculation of these terms starting from an elegant geometrical treatment of branes in eleven dimensional supergravity.

Robert William Moerman

Scattering amplitudes are the basic building blocks of any quantum field theoretic description of nature. Within the context of perturbation theory, these objects are traditionally computed as an expansion in Feynman diagrams. Feynman diagram calculations have been tremendously successful in particle physics predictions, but they have drawbacks: they introduce redundant, off-shell degrees of freedom which make intermediate computations cumbersome, and which obfuscate the structure and simplicity of the final result.

In this talk, I will give a high-level overview of some of the remarkable developments of the last 10 years which have revolutionised the study of scattering amplitudes. Specific attention will be given to the topic of positive geometries, where scattering amplitudes are encoded as the “volume” of a generalization of projective polytopes called amplituhedra. I will also give a summary of recent results from my PhD research: [arXiv:2002.07146], [arXiv:2003.13704], [arXiv:2010.15858].

David Peinador-Veiga

Queen Mary University of London

The Double Copy is a set of relations between scattering amplitudes in gauge and gravity theories, the first of which appeared in the context of string theory. In a certain sense, the gravity amplitudes are the "square" of gauge theory amplitudes. Similarly, there exists a "squaring" relation for certain families of exact classical solutions, indicating that the double copy could hold beyond perturbation theory. However, it was not clear whether the perturbative quantum double copy and the exact classical one had the same origin. In this talk, I will show how to reconcile these two worlds by exploring the classical limit of amplitudes in (2,2) signature.

AdS/CFT

Ellie Harris

King's College London

Gravity in three spacetime dimensions can be shown to be classically equivalent to Chern-Simmons theory. Using some of the topological properties of Chern-Simons theory, we can calculate contributions to the entropy of the cosmological horizon by considering manifolds that are related to the static patch of de Sitter.

Michele Santagata

University of Southampton

Scattering amplitudes are very important objects in physical theories. They are observables and, more importantly, unveil deep aspects of theories such as symmetries - which are sometimes hidden in a Lagrangian formulation. In this talk I will show some recent developments on the scattering of four-closed strings in AdS_5 X S^5, dual - via AdS/CFT - to the four-point function of half-BPS operators in N=4 SYM. The results suggest a close relation between AdS and flat space scattering amplitudes yet to be fully understood.

Aaron Poole

University of Southampton

In this talk I will discuss charges in asymptotically locally de Sitter spacetimes. I will begin by motivating this work within the broader goal of developing a framework for gravitational waves in de Sitter for full nonlinear general relativity. I will then review the asymptotics of de Sitter spacetimes, before showing that one can use the tools of the covariant phase space formalism, together with techniques from AdS/CFT, to derive expressions for conserved quantities.

Lattice field theory

Ryan Hill

University of Southampton

Precision tests of the unitary of the CKM matrix are promising avenues in the search for new physics. The desire for additional determinations of the matrix element |V_{ub}| and a long-standing 2-3 σ discrepancy between results from inclusive B to X_u and exclusive B to π processes motivate the study of QCD B to π semileptonic form factors on the lattice. The status of our preliminary B to π l ν results will be discussed by highlighting updates to our analysis. The final results of this project will provide updates to the 2015 RBC/UKQCD B to π l ν result.

Ben Kitching Morley

University of Southampton

ΛCDM is a highly successful empirical cosmological model that describes observational data remarkably well. The part describing the very early Universe is based on cosmic inflation, which is however an effective theory that cannot fully describe the strongly-coupled gravity regime of the initial big-bang singularity. An alternative theory, Holography Cosmology, has shown great promise in tackling this issue, while fitting observational data equally well. This theory, and its study through lattice computations, will be the subject of my talk.

Phenomenology

Joe Davies

Queen Mary University of London

Dark Matter has been one of the most difficult to solve problems in physics for decades. Previous methods have, so far, made for slow (albeit continual) progress. With the advent of Machine Learning use in Physics and it's growing popularity, the Dark Machines Group at ATLAS have begun to use sophisticated ML algorithms in order to find an answer to one of the Universe's greatest mysteries. I will take you through the group and the kind of algorithms we use, the methods in applying them and what the future may hold for the intersection between AI and Physics.

Shubhani Jain

University of Southampton

We present a novel approach to study the performance of different jet-clustering algorithms in the presence of different resolution parameters and reconstruction procedures for b-jets from Beyond the Standard Model (BSM) Higgs Bosons.

Model building

Adrian Padellaro

Queen Mary University of London

Recent work by Kartsaklis, Ramgoolam, Sadrzadeh, Sword on random matrix theory discovered that Gaussian matrix distributions with permutation symmetry are good statistical models of words within the framework of compositional distributional semantics. Particular interest lies in the moments of permutation invariant polynomials in matrix variables. It is known that permutation invariant matrix polynomials are in correspondence with directed graphs. We illustrate how directed graphs on the other hand correspond to double cosets of permutation groups. The two-step duality culminates in a group theoretical scheme for constructing the moments of permutation invariant matrix polynomials of any degree. We describe the generalization to two-matrix models, which involves 2-colored directed graphs.

George Barnes

Queen Mary University of London

In recent work Kartsaklis, Ramgoolam and Sadrzadeh developed a class of free matrix models for which the usual U(N) symmetry is relaxed to a less restrictive S_N, the group of permutations. Utilising the combinatorics of Wick contractions from QFT and representation theory helps to uncover the rich mathematical structure of these models and permits the computation of expectation values of the most general permutation invariant Gaussian theories. An application of these models to the statistics of words in computational linguistics is described. This application was central in motivating the development of these models and, more recently, provided the stimulus for extending this programme to include two-matrix models.

Bowen Fu

University of Southampton

We study the connection between the two indications of physics beyond the Standard Model (SM): the masses and mixing of neutrinos and the existence of dark matter (DM). To have a more testable connection, we consider a minimal type Ib seesaw model instead of the traditional type I seesaw model. In the minimal type Ib seesaw model, the effective neutrino mass operator involves two different Higgs doublets and two right-handed neutrinos which form a single heavy Dirac pair. To account for DM, we consider neutrino portal couplings to a dark fermion and a dark scalar. We explore the parameter space of the extended model consistent with both oscillation data and DM relic abundance. Within this framework, we show how DM can be directly related to laboratory experiments when the heavy Diracneutrino mass is around 1~100 GeV.

Detector physics

Meirin Oan Evans

University of Sussex

Machine Learning to probe a rare LHC process

I want to make measurements of a rare LHC signal process - the production of a top quark, antitop quark and Z boson at the same time. Background processes that look similar to the rare signal process are much more common. A machine learning technique can optimise at the same time the use of many variables that separate signal and background. Using machine learning, signal and background are separable and measurements of the rare process can be made, allowing for stringent tests of the Standard Model of particle physics.

Henry Day-Hall

University of Southampton

Machine Learning to probe a rare LHC process

Spectral Clustering as a means of jet formation and IRC safety. Spectral clustering, developed by the machine learning community, has proven to be a powerful and versatile clustering method. Jet clustering, particularly in the case of a boosted topology, is a key problem for particle identification in experimental physics. If spectral clustering can be shown to be suitable for the task it might enable us to extract more information from the data we generate.

A key factor for the suitability of an clustering algorithm is infrared and collinear (IRC) safety. While there are algorithms that are not IRC safe, the most popular algorithms are. To be viable for use in QCD calculations the jet formation algorithm must be IRC safe.

Flexability to cluster data with differing hard processes is also a great asset for a clustering algorithm. The performance of spectral clustering on multiple data samples should also be compared.

In this talk I will discuss the mechanics, performance and the IRC safety of spectral clustering.