Triangle Seminars

Abstract:
There are many reasons to consider perturbative QFT around curved backgrounds, but it is often difficult to perform explicit computations in these settings. Progress in the study of scattering amplitudes (around a trivial background) suggests alternative perspectives to space-time Lagrangians and Feynman rules which could enable progress in the study of scattering on curved backgrounds. I will discuss one such alternative, known as double copy, with a particular focus on gluon and graviton scattering around non-linear plane wave backgrounds

Abstract:
I will review analytic SU(2) Yang-Mills solutions with finite action on de Sitter space from a new perspective. As a byproduct, all abelian solutions are classified and related with rational electromagnetic knots. In the Yang-Mills case, the gravitational backreaction is easily taken in to account as well.

Abstract:
This talk will explore topological invariants of susy
gauge theories, with some emphasis on index-like
quantities and the notion of holonomy saddles.

We start with 1d refined Witten index computations
where the twisted partition functions typically show
rational, rather than integral, behavior. We will explain
how this oddity is a blessing in disguise and propose
a universal tool for extracting the truely enumerative
Witten indices. In part, this finally put to the rest
a two-decade-old bound state problems which had
originated from the M-theory hypothesis.

Along the way, we resolve an old and critical conflict
between Kac+Smilga and Staudacher/Pestun, circa
1999~2002, whereby the notion of holonomy saddles
emerges and plays a crucial role. More importantly,
the holonomy saddle prove to be universal features
of supersymmetric gauge theories when the spacetime
include a small circle. We explore them further for
d=4, N=1 theories, with much ramifications on recent
claims on Cardy exponents of their partition functions.

Abstract:
I will first review the Batalin-Vilkovisky formalism and its mathematical foundations with an emphasis on higher algebraic structures and classical field theories. I will then move on and discuss recent developments in formulating higher gauge theory with Lie quasi-groupoids as gauge structure. Finally, I will explain how all these ideas can be combined with those of twistor theory to formulate maximally superconformal gauge theories in four and six dimensions by means of quasi-isomorphisms.

Abstract:
I will talk about the formalism of supersymmetric localization in supergravity using the deformed BRST algebra defined in the presence of a supersymmetric background. The gravitational functional integral localizes onto the cohomology of a global supercharge
Q_eq, obeying
(Q_eq)²=H, where
H is a global symmetry of the background. This construction naturally produces a twisted version of supergravity whenever supersymmetry can be realized off-shell. I will present the details of the twisted graviton multiplet and ghost fields for the superconformal formulation of four-dimensional N=2 supergravity. As an application of our formalism, we systematize the computation of the exact quantum entropy of supersymmetric black holes. In particular, we compute the one-loop determinant of the Qeq deformation operator for the off-shell fluctuations of the Weyl multiplet around the
AdS₂×S² saddle.

Abstract:

A four-dimensional abelian gauge theory can be coupled to a 3d CFT with a U(1) symmetry living on a boundary. This coupling gives rise to a continuous family of boundary conformal field theories (BCFTs) parametrized by the gauge coupling Ï„ and by the choice of the CFT in the decoupling limit. Upon performing an Electric-Magnetic duality in the bulk and going to the decoupling limit in the new frame, one finds a different 3d CFT on the boundary, related to the original one by Witten's SL(2, Z) action. In particular the cusps on the real Ï„ axis correspond to the 3d gauging of the original CFT. We study general properties of this family of BCFTs. We show how to express bulk one and two-point functions, and the hemisphere free-energy, in terms of the two-point functions of the boundary electric and magnetic currents. Finally, upon assuming particle-vortex duality (and its fermionic version), we show how to turn this machinery into a powerful computational tool to study 3d gauge theories.

Abstract:
We probe a generic two dimensional conformal interface via a collider experiment. We measure the energy and charges which are reflected and transmitted through the interface. We find that the average transmitted energy is independent of the way the state is
constructed and determined by the central charge and a single piece of CFT data. We comment on the universality of the result and discuss some examples.

Abstract:
In the first part of my talk I will give a brief introduction to the main features of the Entaglement Entropy of a bipartite system in Integrable Quantum Field Theories and Conformal Field Theories. Secondly I will discuss the results my collaborators and I obtained in our two papers. In particular, I will consider the Entaglement Entropy of a single connected region of a finite bipartite system in excited states described by one-dimensional massive free theories with finite numbers of particles. I will show that in the limit of large volume and large length of the region the excess of entanglement due to the presence of the particles with respect to the ground state takes a simple form and admits a "q-bit interpretation".

Abstract:
This will be presenting mainly some of my recent work, and also aspects of recent work of Herbert Spohn, both developed in parallel. The classical Toda system is a one-dimensional integrable many-body system, which can be seen either as a gas of particles or as a chain of degrees of freedom. Herbert has shown how the generalised Gibbs ensembles of the Toda chain can be obtained from a certain limit of the beta-ensemble in random matrix theory. Analysing and connecting the gas and chain viewpoints, I have obtained both the generalised Gibbs ensembles and generalised hydrodynamics from a quasiparticle scattering description. Thus we make a connection between quasiparticle scattering and random matrix theory.

Abstract:
I will discuss some old and new relations between the characters, modular data and braiding and fusing matrices of rational conformal field theories and their
associated modular tensor categories. These relations involve concepts from number theory which I will explain in the talk.