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.
Tarek Anous
The discreet charm of the discrete series in dS
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
Lakshya Bhardwaj
Generalized Charges and their Physical Applications
I will discuss how generalized (non-invertible or categorical) symmetries act on operators in a quantum field theory. Although the structure of non-invertible symmetries, like their composition rules, has been well-researched over the last couple of years, the action of these symmetries on physical operators had remained poorly understood until recently. This gap was filled in a recent paper 2305.17159 (see also 2305.17165 for related work), and this talk is partly based on that. The various possible actions of generalized symmetries on operators are referred to as generalized charges. The understanding of these charges opens the door for physical applications of generalized symmetries. I will illustrate this with a discussion of how gapped phases of quantum field theories are constrained by the presence of generalized symmetries, in particular obtaining rather stringent constraints on gapped phases in 1+1 spacetime dimensions. Extending the Landau-Ginzburg paradigm, these phases are characterized by order parameters carrying generalized charges.
Matthew Buican
Some Applications of Free Supersymmetric Fields
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.
James Drummond
String/Supergravity Loops in AdS from CFT
Amihay Hanany
Symplectic singularities, Phase diagrams, and Magnetic Quivers
Over the past 10 years we faced an impressive progress in the understanding of theories with 8 supercharges. This was through the introduction of theoretical tools which help analyze hypermultiplet moduli spaces in a whole host of gauge theories. Coulomb branches of 3d N=4 theories are now computed very easily through the so called “monopole formula”.The resulting moduli spaces are symplectic singularities which are characterized into different families — closures of nilpotent orbits, intersections of Slodowy slices, orbifolds, slices in the affine Grassmanian, and more. All these names should henceforth enter the physics vocabulary in studies of theories with 8 supercharges. The phase diagrams of symplectic singularities give a further characterization. They are computed with the help of combinatorial tools such as quiver subtraction. This helps distinguish simple/complicated moduli spaces and extends the notion of the Higgs mechanism to theories that admit no Lagrangians. A major ingredient in the success of the recent progress is the use of brane systems for theories with 8 supercharges. Magnetic quivers are computed using these brane systems, and solve long standing problems in finding Higgs branches in regimes where Lagrangian techniques are not available. This sheds light on tensionless strings in 6d, massless instantons in 5d and Argyres Douglas theories in 4d. The talk aims to review the progress in understanding theories with 8 supercharges and to give a taste to the new tools and to the new terminology that rose as a result of this study.
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
Low-supersymmetry exact D-instanton corrections from String Field Theory
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 Torielli
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
Higher operations in TQFTs (or Massey products for lcPFAs)
Prefactorisation algebras (PFAs) axiomatise the algebraic structure of observables in QFTs. They are typically valued in cochain complexes, when the QFT is described using the BV/BRST formalism. In this talk I will focus on locally constant (lc) PFAs which correspond to Topological QFTs. I will describe how to obtain the induced algebraic structure on the gauge invariant observables of the TQFT, i.e. on the cohomology of the lcPFA. This involves an ordinary associative, unital product but typically also "higher" operations known as Massey products.
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.
