Spring 2020

KCL Strings Journal Club Spring 2020

Included page "clone:kclstrings" does not exist (create it now) Spring 2020 Journal Club Here's a summary of all the activity of our Journal Club during the Spring 2020 term.

Summary

May 22: Andrea Cavaglia Title: The proof of the Averaged Null Energy Condition using Quantum Information Abstract: The ANEC is a positivity constraint on a null-ray integral of the stress-energy tensor in relativistic unitary quantum field theories. As a follow-up to Maxime's journal club two weeks ago, I will present the alternative proof of the ANEC found in hep-th/1605.08072 using ideas of quantum information. The proof involves a quantity called Relative Entropy, and its property of Monotonicity. I will introduce these concepts in the finite-dimensional case, and discuss the extension to QFT. Then I will describe the computation of 1605.08072, where the Relative Entropy between a state and the vacuum is computed on a half-space, and on a deformed half-space. The monotonicity property then will lead to the ANEC. May 15: Giuseppe Del Vecchio Del Vecchio Title: Random Unitary Circuits and Black Holes Abstract: As pointed out by Hawking, evaporating black holes seem to be inconsistent with the unitarity of quantum physics raising up what is known as black hole information paradox. Few years ago, Hayden and Preskill, based on quantum information theoretic concepts, described the possibility for information not to be lost in a black hole (arXiv:0708.4025v2). At the same time, in the low energy world, random unitary circuits have found great applications in understanding entanglement growth and operator spreading in quantum many body systems. The talk will be divided in three parts: first, I will introduce basic language of information theory, then I will review the Hayden-Preskill evaporation protocol and to close I will discuss a recent implementation of a random unitary circuit aiming to emulate the evaporation and exhibiting a Page curve for the entropy of the black hole (arXiv:2002.09236v2). May 1: Maxime Trepanier Title: Average null energy condition from causality Abstract: I will review the proof of the average null energy condition in conformal field theory following https://arxiv.org/abs/1610.05308. The proof is based on a careful analysis of the implications of causality and unitarity on euclidean correlators, and nicely ties together many old ideas in a new way. Time permitting, I will also discuss how the ANEC can be applied to derive conformal collider bounds. April 24: Rishi Mouland Title: Light cone methods in QFT and M-theory Abstract: I will discuss the long and winding history of light cone methods in high energy physics, starting with the foundational work of Dirac on light cone quantisation and Weinberg on the infinite momentum frame. I will explain some of the issues along the way, not least the infamous zero mode problem, and outline their successful resolutions - most famously discrete light cone quantisation (DLCQ). After describing the wealth of applications of DLCQ in QFT - particularly in QCD - I will give a pedagogical introduction to the M(atrix) Theory conjectures of BFSS, from which one obtains a matrix model description of a particular light cone limit of M-theory. Finally, time permitting, I hope to discuss some more recent developments in formulations and applications of light cone limits in QFT and M-theory. Slides here April 17: Reimer Kühn (Disordered Systems Group) Title: Overview on dynamics of contagions on networks April 3: Leonel Quinta Queimada CANCELLED Title: Recovering the spacetime metric from a holographic dual Abstract: I will try to provide an overview of the papers 1605.01070, 1612.00391 and most recently 2003.08409, where progress is made in determining how the bulk metric of a holographic spacetime can be reconstructed purely from boundary data. My focus will be in the results of the first reference 1605.01070, which provides the framework for the other works. March 27: Alejandro Cabo-Bizet Title: Toward an Effective CFT2 from N = 4 Super Yang-Mills and Aspects of Hawking Radiation Abstract: I will discuss the recent paper 2003.02770 with the title above (by J. Nian and L. Pando Zayas). March 20: Benjamin Doyon Title: Emergent hydrodynamics in integrable systems Abstract: Typical systems of many particles in strong interaction have extremely complex behaviours which are hard to study in detail. But when the system is very large, simplicity resurfaces: typically just a few degrees of freedom are relevant, which follow new, simple laws. Understanding what the emergent behaviours are from the underlying microscopic interactions is one of the foremost problems in modern science. A very powerful set of ideas and tools at our disposal is hydrodynamics. Although the Navier-Stokes and related equations have been studied for a very long time, we are now starting to uncover the full potential of the fundamental principles of hydrodynamics. In particular, in a recent breakthrough it was understood how to apply these principles to quantum and classical integrable models, where infinitely many conserved currents exist, giving ``generalised hydrodynamics”. I will overview the fundamental principles of hydrodynamics and their adaptation to integrable systems, with simple examples such as the quantum Lieb-Liniger model, the classical Toda model, and the soliton gases. I will discuss a recent cold-atom experiment that confirmed generalised hydrodynamics, and, if time permits, show some of the exact results that can be obtained with this formalism, such as exact nonequilibrium steady states and exact asymptotic of correlation functions at large space-time separations. March 13: Kento Osuga (Sheffield) Title: Supersymmetric Topological Recursion Abstract: Topological recursion is a powerful abstract recursive formalism whose applications, somewhat surprisingly, appear in both physics and mathematics such as 2d quantum gravity and Gromov-Witten invariants. Then an interesting question arises: does a similar story hold with supersymmetry? In this talk, I will discuss the structure underlying topological recursion and show an interesting relation to vertex operator algebras which naturally leads us to the notion of supersymmetric topological recursion. If time permits, I will discuss potential applications of super topological recursion. This is joint work (in progress) with Vincent Bouchard. March 6: Edgar Shaghoulian (Cornell) Title: TTbar deformations in Quantum Mechanics Abstract: Based on https://arxiv.org/abs/1907.04873 and https://arxiv.org/abs/1912.06132 February 14 - March 4: Black Hole Information Journal Club Summary of talks, speakers and references can be found here. February 7: Masanori Hanada (Southampton) Title: The simplest toy model for holographic black hole Abstract: I show that gauged Gaussian matrix model — which is trivially integrable — captures various important features of confinement/deconfinement transition, and hence, a good toy model for black hole via gauge/gravity duality. Because this model is solvable, we can demonstrate a novel phenomenon, “partial deconfinement”: SU(M) subgroup of SU(N) deconfines, where M grows from 0 (complete confinement) to N (complete deconfinement). It is natural to expect that the completely deconfined phase is dual to the large black hole, and the partially deconfined phase is dual to the small black hole. If the time permits, I will explain the close connection (or I would say “equivalence”) between confinement and Bose-Einstein condensation. This talk is based on https://arxiv.org/abs/1909.09118 and https://arxiv.org/abs/2001.10459. Papers discussed: Lense–Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system January 24: Imtak Jeon Title: One-loop determinants for black holes in 4d gauged supergravity Abstract: I will review about the recent paper http://arxiv.org/abs/arXiv:1908.05696 by Kiril Hristov, Ivano Lodato and Valentin Reys, where they use supersymmetric localization in supergravity for the entropy of supersymmetric black hole in asymptotic AdS4 space. I will present the main result and what is not yet understood for application of localization method in gauged supergravity. Papers discussed: Lecture notes on Generalised Hydrodynamics (Benjamin) Duality and Transport for Supersymmetric Graphene from the Hemisphere Partition Function (Chris, Imtak, et al) Colour-Twist Operators I: Spectrum and Wave Functions (Andrea, Kolya, et al) Twisted form hierarchies, Killing-Yano equations and supersymmetric backgrounds (George)