Past Relativity Seminar

7 February 2017
12:00
Dr Michal Wrochna
Abstract

An essential ingredient of AdS/CFT, dS/CFT and other dualities is a geometric notion of scattering that refers to asymptotics rather than, say, infinite time limits. Though one expects non-perturbative versions to exist in the case of linear quantum fields (and non-linear classical fields), this has been rigorously implemented in Lorentzian settings only relatively recently. The goal of this talk will be to give an overview in different geometrical setups, including asymptotically Minkowski, de Sitter and Anti-de Sitter spacetimes. In particular I will discuss recent results on classical scattering and particle interpretations, compare them with the setup of conformal scattering and explain how they can be used to construct "in-out" Feynman propagators (based on joint works with Christian Gérard and András Vasy).

17 January 2017
12:00
to
13:15
Lance Dixon
Abstract

Amplitudes in planar N=4 SYM are dual to light-like polygonal Wilson-loop expectation values. In many cases their perturbative expansion can be expressed in terms of multiple polylogarithms which also obey certain single-valuedness conditions or branch cut restrictions. The rigidity of this function space, together with a few other conditions, allows one to construct the six-point amplitude -- or hexagonal Wilson loop -- through at least five loops, and the seven-point amplitude through 3.5 loops. Then one can "fold" the polygonal Wilson loops into multiple degenerate configurations, expressing the limiting behavior in terms of simpler function spaces, and learning in the process about how amplitudes factorize.
 

29 November 2016
12:00
to
13:15
Glenn Barnich
Abstract

After a brief review of holographic features of general relativity in 3 and 4 dimensions, I will show how to derive the transformation laws of the Bondi mass and angular momentum aspects under finite supertranslations, superrotations and complex Weyl rescalings.
 

22 November 2016
12:00
Federico Zerbini
Abstract

The Feynman diagram expansion of scattering amplitudes in perturbative superstring theory can be written (for closed strings) as a series of integrals over compactified moduli spaces of Riemann surfaces with marked points, indexed by the genus. Therefore in genus 0 it is reasonable to find, as it often happens in QFT computations, periods of M_{0,N}, which are known to be multiple zeta values. In this talk I want to report on recent advances in the genus 1 amplitude, which are related to the development of 2 different generalizations of classical multiple zeta values, namely elliptic multiple zeta values and conical sums.

8 November 2016
12:00
to
13:15
Dr Christian Vergu
Abstract

In this talk I will present a class of super-Wilson loops in N=4 super Yang-Mills theory. The expectation value of these operators has been shown previously to be invariant under a Yangian symmetry. I will show how the kinematics of such super-Wilson loops can be described in a twistorial way and how this leads to compact, manifestly super-conformal invariant expressions for some two-point functions.
 

1 November 2016
12:00
to
13:30
Paul Fendley
Abstract


I will survey of some of the many significant connections between integrable many-body physics and mathematics. I exploit an algebraic structure called a fusion category, familiar from the study of conformal field theory, topological quantum field theory and knot invariants. Rewriting statistical-mechanical models in terms of a fusion category allows the derivation of combinatorial identities for the Tutte polynomial, the analysis of discrete ``holomorphic'' observables in probability, and to defining topological defects in lattice models. I will give a little more detail on topological defects, explaining how they allows exact computations of conformal-field-theory quantities directly on the lattice, as well as a greatly generalised set of duality transformations.
 

19 July 2016
12:00
to
13:15
Dr Olaf Hohm
Abstract

I review work done in collaboration with Siegel and Zwiebach,  in which a doubled geometry is developed that provides a spacetime  action containing the standard gravity theory for graviton, Kalb-Ramond field and dilaton plus higher-derivative corrections. In this framework the T-duality O(d,d) invariance is manifest and exact to all orders in $\alpha'$.  This theory by itself does not correspond to a standard string theory, but it does encode the Green-Schwarz deformation characteristic of heterotic string theory  to first order in $\alpha'$ and a Riemann-cube correction to second order in  $\alpha'$. I outline how this theory may be extended to include arbitrary string theories. 

 

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