Triangle Seminars

Abstract:
String theory has been remarkably successful in explaining the microscopic origin of the entropy of certain black holes, primarily supersymmetric ones. However, finding the microscopic description of more realistic black holes remains a challenging open problem. In this talk, I will review evidence suggesting that the microscopic description of near- and non-extremal black holes is governed by special irrelevant deformations of two-dimensional conformal field theories. I will then discuss the properties of a particular class of solvable irrelevant deformations of two-dimensional quantum field theories, known as TT– and JTˉJ\bar-deformed CFTs. Finally, I will discuss the lessons that recent progress in understanding these deformations offers for the microscopic description of general black holes.

Abstract:
Effective field theories in particle physics are typically developed for clean, isolated systems, yet many physical phenomena, from condensed matter to gravitating systems, involve noisy and dissipative environments. The Schwinger-Keldysh formalism provides a powerful framework for describing such non-equilibrium dynamics and has led to important advances in areas including black hole physics, dissipative hydrodynamics, non-equilibrium holography, and primordial cosmology. I will begin with a pedagogical introduction to open-quantum-system techniques formulated within the Schwinger–Keldysh path integral. I will show how symmetries, locality, and unitarity constrain dissipation and noise, and illustrate the framework by deriving the imprints of dissipative dynamics on primordial non-Gaussianities. I will conclude by discussing the challenge of formulating general relativity in the presence of an unspecified medium.

Abstract:
I will discuss scattering on the Coulomb branch of planar N=4 SYM at finite ’t Hooft coupling. This describes a family of classical open-string S-matrices that smoothly interpolates between perturbative parton scattering at weak coupling and flat-space string scattering at strong coupling. I will focus on the four-point amplitude and discuss its remarkably rich structure: nonlinear Regge trajectories, dual conformal invariance, an intricate spectrum of bound states with an accumulation point, and a two-particle cut. Using dispersion relations and S-matrix bootstrap techniques, these properties can be incorporated to constrain the amplitude at finite ’t Hooft coupling, and I will discuss bounds on Wilson coefficients, couplings to bound states, and the overall shape of the amplitude.
This talk is based on https://arxiv.org/abs/2510.19909.

Abstract:
The past few years have seen major advances in understanding the properties of axions in string theory. This progress is thanks to new computational tools that allow for fast and automated calculations with Calabi-Yau manifolds. I will describe the predictions string theory makes for axion masses, decay constants, and axion-photon couplings, and how these depend precisely on the topology of the Calabi-Yau. I will describe explicit constructions of millions of axiverse models on Calabi-Yaus with Hodge numbers up to 491, across the whole Kreuzer-Skarke database (and some results beyond this). Phenomenology computed includes: black hole superradiance, dark matter relic density, fuzzy dark matter, decaying heavy relics and the intergalactic medium, and the QCD axion mass. I will describe the correlation between QCD axion mass and topology, and how this makes it possible for axion "haloscope" experiments to experimentally infer Hodge numbers, divisor topologies, and moduli space loci. I demonstrate the statistical state of the art by computing a full forward model incorporating likelihoods from the cosmic microwave background and Lyman-alpha forest and find the maximum Bayesian posterior probability region on the moduli space of a given CY favoured by a resolution of the tension in these data by an ultralight axion composing 1% of the dark matter. 

Abstract:
The gravitational Compton amplitude describes gravitational waves scattering off a single black hole and is therefore a one-body observable ideal for analyzing quadratic-in-curvature of generic (Kerr) black holes from an effective field theory point of view. Based on upcoming work together with Y. Fabian Bautista, Gustav Jakobsen, and Kays Haddad, in this talk, I will discuss what makes it worth studying and calculating explicitly. I briefly review elements of black hole perturbation theory, which is the UV theory that describes such objects. I will then explain how worldline quantum field theory (WQFT) is an ideally suited tool to calculate the amplitude, focusing on similarities between this and the gravitation two-body problem which has recently been pushed to four loops. Finally, I will illustrate our matching procedure between these two theories, which allows us to calculate the Love numbers of black holes, with a particular focus on the N-matrix (Magnusian).