Jan Albert (Princeton) | Form factors in the large-N bootstrap | November 19, 2025
Well after 50 years since the discovery of QCD, we are still lacking a description of the theory of strong interactions at low energies. For instance, we do not know how to produce the rich meson spectrum out of the handful of parameters in the QCD Lagrangian, other than by brute-force lattice simulations. This has prompted a revival of the S-matrix bootstrap, which aims to single out the theory as the unique set of scattering amplitudes consistent with certain self-consistency conditions. This approach has led to sharp, rigorous bounds for pion scattering in the large N limit. But these bounds are completely agnostic about the UV completion of the theory. In this talk I will explain how, by enlarging the system to include form factors and two-point functions, one can input UV information (computed with perturbative QCD) into the bootstrap. We will see how this improves upon the previous bounds.
Benjamin Lehmann (MIT) | Broadening direct searches for light dark matter | November 12, 2025
Direct searches for low-mass DM were originally designed using the same conceptual picture as WIMP searches. However, over the last five years, the crucial role of in-medium effects has come into sharp focus. A new theoretical framework in the language of condensed matter physics has emerged for understanding the relationship between the properties of detector systems and their sensitivity to DM interactions. I will report on three recent advances that leverage this formalism to substantially broaden the design considerations for the next generation of experiments, and even extract new constraints from existing data. First, for DM–electron interactions, large new datasets generated by the materials science community have enabled the first data-driven search for optimal detector materials, which promises to significantly enhance the sensitivity of near-future experiments. Second, just as detectors designed to detect nuclear scattering have been used to study electronic scattering, I will explain how in-medium effects make the reverse possible as well, allowing us to set new limits on DM–nucleon scattering using the low-threshold detectors designed to detect electronic scattering. Third, with the advent of low-threshold detectors sensitive to energy deposits as low as 50 meV, we have finally entered the regime where the interaction rate can be significantly enhanced due to the geometry of the detector system. These three considerations promise to substantially accelerate the search for light DM in both mass and cross section over the coming years.
Ji Hoon Lee | AdS3 Quantum Gravity and Finite N Chiral Primaries | October 29, 2025
String theory on AdS3 x S3 x M4 provides a well-studied realization of AdS3/CFT2 holography, but its non-perturbative structure at finite N ~ 1/G_N is largely unknown. A long-standing puzzle concerns the stringy exclusion principle: what bulk mechanism can reproduce the boundary expectation that the chiral primary Hilbert space of the symmetric orbifold contains only a finite number of states at finite N?
In this talk, we present a bulk prescription for computing the finite N spectrum of chiral primary states in symmetric orbifolds of T4 or K3. We show that the integer spectrum at any N is reproduced exactly by summing over one-loop supersymmetric partition functions of the IIB theory on (AdS3 x S3)/Z_k x M4 orbifolds and their spectral flows. Using the worldsheet in the tensionless limit, we verify that the terms appearing in our proposal coincide with the supersymmetric partition functions of these orbifold geometries. These partition functions contribute with alternating signs due to BPS modes with negative conformal dimensions and charges in twisted sectors. The resulting alternating sum collapses via large cancellations to the finite N polynomials observed in symmetric orbifold CFTs, providing a bulk explanation of the stringy exclusion principle. We identify different Stokes sectors where different infinite subsets of these geometries contribute to the path integral, and propose a classification as functions of the chemical potentials.
Giulia Isabella (UCLA) | Love number matching: uncovering the simplest EFT | October 22, 2025
At wavelengths large compared to the source size, any compact object admits a point-particle EFT whose finite-size effects are encoded by Love numbers. In this talk I will discuss a novel method to compute gravitational wave amplitudes by reinterpreting the Feynman diagram expansion as a Born series, solution of an effective wave equation. This method enables efficient, systematic calculations of scattering amplitudes off any compact object, yielding new predictions for scalar black-hole Love numbers and their renormalization-group equations up to O(G^7).
Dan Carney (UC Berkeley) | Testing quantum gravity | October 15, 2025
I will give an overview of proposals to test the quantization of the gravitational field using terrestrial experiments. This will include entanglement experiments, searches for noise in gravitational wave interferometers, and "single-graviton detection" experiments. As a particular example of a non-standard gravity model that could be tested, I will discuss a recent phenomenological model of "entropic gravity" and its experimental signatures.
Maximilian Ruhdorfer | Exploring QCD-like Dynamics from Supersymmetry | October 8, 2025
Understanding the mechanisms of confinement and the dynamics of low-energy QCD remains one of the central open problems in the Standard Model. In this talk, I will describe how these issues can be explored in a close relative of QCD, constructed by starting from supersymmetric QCD and systematically breaking supersymmetry through anomaly mediation. These models reproduce the same phases as ordinary QCD, while allowing us to probe confinement from a different dynamical perspective. Within this framework, one can compute the η′ potential, study θ-dependence, and analyze the phase structure associated with spontaneous CP violation at θ = π. Moreover, the construction permits a derivation of the analog of the chiral Lagrangian, enabling explicit tests of the size of a dynamically generated up-quark mass. Strikingly, we find that in these models the generated contribution could be large enough to account for the full observed up-quark mass.
Ross Dempsey | Bootstrapping Holographic Theories | October 1, 2025
Holographic conformal field theories provide a window into quantum gravity. However, these field theories are difficult in their own right, and to make progress on them we need new non-perturbative methods. I will describe a general technique for combining the conformal bootstrap method with constraints from supersymmetric localization. This dramatically improves the ability of the bootstrap to constrain holographic theories. I will describe results for N = 4 super-Yang-Mills theory, for which this technique enables qualitatively new studies of observables as a function of the Yang-Mills coupling. I will also describe substantial improvements in the bootstrap of 3D ABJM theory, which enables a precise numerical study of higher-derivative corrections in M-theory.
Pratik Rath | Living on the edge: a non perturbative resolution to the negativity of bulk entropies | September 24, 2025
In this talk, I will discuss two entropic puzzles in JT gravity and their resolution, which requires taking into account non-perturbative effects in the gravitational path integral. In JT gravity, which is dual to a random matrix ensemble, the gravitational thermal entropy becomes negative at very low temperatures. This puzzle arises when computing the annealed (instead of quenched) entropy, corresponding to an incorrect averaging procedure in the dual matrix model. After defining an “intermediate” quantity, the semi-quenched entropy, I will explain how the positivity of entropy can be rescued. From the bulk perspective, both a resummation of higher-genus topologies and wormhole effects are crucial. From the matrix model perspective, the resolution relies on the statistics of eigenvalues near the edge, governed, in different regimes, by the Airy distribution or by 1-eigenvalue instantons. A related puzzle arises where the entanglement entropy across a two-sided black hole can become negative when inserting a large number of matter excitations behind the black hole horizon. First posed by Lin, Maldacena, Rosenberg, and Shan in two-sided BPS black holes in SUSY JT gravity, I will show this paradox extends to non-SUSY JT gravity with matter as well and demonstrate how positivity is rescued in both cases. Finally, I will discuss a tensor network toy model with the same features.
Matthew Heydeman (Harvard) | BPS Black Holes in AdS3xS3xS3xS1 and Beyond | September 17, 2025
The Bekenstein–Hawking formula gives a coarse-grained count of the number of microstates of a black hole, and it is remarkable that it may sometimes be reproduced from a microscopic count in string theory. However, the standard approach neglects quantum effects in the bulk which lead to pathologies for both supersymmetric and non-supersymmetric black holes, such as the breakdown of thermodynamics at sufficiently low temperatures.In this talk, we will explain how a more careful treatment of the gravitational path integral resolves these tensions and leads to new and surprising effects that are completely invisible classically.For extended supersymmetry, we will find that physically sensible black holes can preserve at most 4 supercharges, with the most exceptional example being black holes in AdS3xS3xS3xS1. This notoriously poorly understood background in string theory has a nonlinear large N=4 superconformal symmetry, but we are nevertheless able to make novel predictions for the BPS and near-BPS spectrum from gravity. Notably, we find discrete jumps in the BPS spectrum as a continuous parameter is adjusted-- a quantum gravity effect for which no microscopic derivation is currently known. This result is corroborated by constructing a family of non-extremal supersymmetric black holes that contribute to a supersymmetric index yet possess a temperature-dependent free energy.
Justin Berman (UM) | S-matrix Bootstrap: Present and Future | September 10, 2025
The modern S-matrix bootstrap carves out the space of 4-point amplitudes compatible with unitarity, causality, and locality. In my talk, I review the current standing and future goals of the bootstrap with an emphasis on three central questions: What features do legal amplitudes have? How can we determine when these 4-point amplitudes extend to n-point S-matrices? To what extent can the bootstrap be applied to amplitudes in the real-world?
