Opening

Amihay Hanany

Matthew Buican

Lotte Hollands: Non-perturbative partition functions for supersymmetric QFT's Recently, a rather elegant picture has emerged for the non-perturbative topological string. In this picture the non-perturbative partition function has a piecewise-constant dependence on an additional phase, and jumps have an interpretation in terms of certain BPS states. In this meeting I will explain these ideas from the perspective of four-dimensional N=2 field theory and its lift to five dimensions, with the four-dimensional Seiberg-Witten theory and the resolved conifold as two main examples. This talk is based on 2109.14699, 2203.08249 and work in progress.

Harvey Reall - Creases, corners and caustics: properties of non-smooth structures on black hole horizons The event horizon of a dynamical black hole is generically a non-smooth hypersurface. I shall describe the types of non-smooth structure that can arise on a horizon that is smooth at late time. This includes creases, corners and caustic points. I shall discuss ``perestroikas'' of these structures, in which they undergo a qualitative change at an instant of time. A crease perestroika gives an exact local description of the event horizon near the ``instant of merger'' of a generic black hole merger. Other crease perestroikas describe horizon nucleation or collapse of a hole in a toroidal horizon. I shall discuss the possibility that creases contribute to black hole entropy, and the implications of non-smoothness for higher derivative terms in black hole entropy. This talk is based on joint work with Maxime Gadioux.

Bogdan Stefanski

Gong show

Tarek Anous - The discreet charm of the discrete series in dS$_2$ Unitarity in de Sitter is mired with potential pitfalls. One of them is that massive particles are represented by (so-called principal series) states with complex conformal dimensions. Even more confusing is that states with positive conformal dimensions and a bounded spectrum, known as the discrete series, are, at the free-field level, represented as scalar tachyons with a finely tuned mass, suggesting that these states mediate some sort of instability. Perhaps this suggests that no consistent field theory can be built with these particle representations. In dS$_2$, however, this can not be the case, as discrete series states arise in the multiparticle spectrum of principal series matter. In this talk I will review some established facts about the discrete series in de Sitter and its quantization. I will then consider models with a particular type of gauge symmetry, where the discrete series makes an appearance in the pre-Hilbert space, but vanishes once the gauge constraints are imposed. Finally I will discuss how this construction can be extended to the case where gravity is dynamical.

Alejandra Castro - Keeping matter in the loop in 3D quantum gravity In this talk I will discuss a novel mechanism that couples matter fields to three-dimensional quantum gravity. This construction is based on the Chern-Simons formulation of three-dimensional gravity, and it centers on a collection of Wilson loops winding around spacetime. We coin this object a Wilson spool. To construct the spool, we build take advantage of representation theory. To evaluate the spool, we adapt and exploit several known exact results in Chern-Simons theory. Our proposal correctly reproduces the one-loop determinant of a free massive scalar field on S^3 and AdS_3 as G_N->0. Moreover, allowing for quantum metric fluctuations, it can be systematically evaluated to any order in perturbation theory.

Lakshya Bhardwaj

Tim Adamo - Fun with strong-field scattering Scattering amplitudes encode the on-shell dynamics of quantum field theories and underpin many physical observables ranging from decay rates to scattering angles. Over the last 30 years, there has been significant progress in developing new methods to calculate scattering amplitudes in perturbation theory around a trivial vacuum, but comparatively little has been learned about scattering in the presence of non-trivial, or 'strong,' background fields. These arise in many important physical scenarios, from lasers to heavy ion collisions to black holes and neutron stars. I will try to convince you that strong-field scattering amplitudes are a playground where perturbative and non-perturbative phenomena meet, presenting important challenges as well as exciting opportunities for theorists.

James Drummond

Andreas Stergiou - Uncovering the Structure of the ε Expansion The ε expansion was invented more than 50 years ago and has been used extensively ever since to study aspects of renormalization group flows and critical phenomena. Its most famous applications are found in theories involving scalar fields in 4−ε dimensions. In this talk, we will discuss the structure of the ε expansion and the fixed points that can be obtained within it. We will mostly focus on scalar theories, but we will also discuss theories with fermions as well as line defects. Our motivation is based on the goal of classifying conformal field theories in d=3 dimensions. We will describe recently discovered universal constraints obtained within the framework of the ε expansion and show that a “heavy handed" quest for fixed points yields a plethora of new ones. These fixed points reveal aspects of the structure of the ε expansion and suggest that a classification of conformal field theories in d=3 is likely to be highly non-trivial.

Alessandro Torrielli - The strange world of AdS2 integrability We will review some of the features of integrable scattering in AdS2 backgrounds, paying particular attention to highlighting the differences with respect to AdS3 and higher dimensions. We will survey some of the progress obtained in the context of massless scattering in AdS2, and the non-standard techniques that enter the game in this case as opposed to the ordinary AdS/CFT methods.

Benoit Vicedo

Ivonne Zavala - Dark Energy in String Theory: from dS to dynamical dark energy In this talk I will first briefly review the status on dS vacua in string theory. I will then discuss recent progress in understanding more generally (early and late time) cosmological acceleration as potential alternative to address current cosmological tensions and present day accelerated expansion of the universe.