Triangle Seminars

Abstract:
This recorded tutorial is available via youtube at https://youtu.be/L-C6Xx0uI3c. The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.

Abstract:
This is the live session included as part of the LonTI lecture on Entanglement in 1+1D Quantum Field Theory. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).

The talk will be structured into three main parts:

First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.

Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.

Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.

Abstract:
I will motivate the possibility that particle Dark Matter (DM) is heavier than the so-called `unitarity limit', of about 100 TeV, and review the proposals to evade it. Among these proposals, I will focus on recent results on supercooled confining phase transitions in the early universe, whose implications are relevant beyond the DM problem. I will finally discuss how these scenarios will be probed at telescopes, underground labs, colliders and gravitational waves detectors.

[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
In this talk I will discuss boundary RG flows for a 4d free scalar field coupled to large N vector models on a 3d boundary. These RG flows connect decoupled fixed points with the free and the critical vector model on the boundary, and they enjoy strong-weak dualities. I will also consider adding gauge fields to the setup.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]

Abstract:
Bootstrap methods have greatly expanded our ability to compute correlation functions in the supergravity approximation. As a result, we now know Mellin space expressions for general half-BPS four-point functions at tree-level in the main holographic CFTs with maximal supersymmetry. These are the \(\mathcal{N} = (2,0)\) theory in six dimensions, \(\mathcal{N} = 4\) Super Yang Mills in four dimensions and \(\mathcal{N} = 8\) ABJM theory in three dimensions. In all three cases, a rich subsector of operators that generate an infinite dimensional symmetry may be constructed by passing to the cohomology of a certain nilpotent supercharge. I will explain the main features of this construction and how they may be accessed holographically. When the protected operators generate a W-algebra, we will see that their four-point functions agree precisely with those predicted by AdS / CFT thus giving a complete check. The other possibility leads us to consider topological quantum mechanics where the calculations are more difficult. Nevertheless, I will show that an infinite family of special OPE coefficients obeys non-perturbative relations that follow from the one-dimensional theory.




https://zoom.us/j/96173937792?pwd=dHNkVVp0T0RtSitFZ2xaUkhqS1VjQT09

Abstract:
[there will be a 30min pre-seminar for students. For zoom link, please contact s.nagyATqmul.ac.uk]
Abstract: Recent work has broadened the scope of scattering amplitudes to include large, classical objects such as the Kerr black hole. This new perspective illuminates surprising aspects of classical gravity, such as the Newman-Janis shift relating Kerr to Schwarzschild. I will describe the connection between amplitudes and classical physics, focussing on the case of Kerr.

Abstract:
The problem of Color Confinement in Yang-Mills theory is one of the deepest problems in theoretical physics. There is convincing numerical evidence from Lattice Gauge Theory, yet the proof of Confinement in Asymptotically Free theories has not been found. I will briefly introduce the Confinement problem and review some results on large N theories using the gauge/gravity duality. I will then discuss two-dimensional SU(N) theory coupled to an adjoint Majorana fermion. I will show that, when the adjoint mass is sent to zero, the spectrum retains a mass gap but the confinement disappears. Using the Discretized Light-Cone Quantization, I will discuss the spectrum of color singlet states and exhibit certain threshold states. Similar threshold states are also present in a model with a massless adjoint and a massive fundamental fermion. They provide new evidence for the lack of confinement. When the adjoint mass is turned on, the theory becomes confining, and the spectrum of bound states becomes discrete. –– Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com/registration.html. The link will be emailed.