Seminars

Title: Detecting chaos in hydrodynamics

Abstract: Hydrodynamics assumes local equilibration and equilibration assumes ergodic mixing driven by chaos — at least in semi-classical systems. For a generic such system the timescales of macroscopic thermalization and onset of microscopic chaos are very different. Nevertheless, it is a pillar of Boltzmann transport that long-time equilibration can be computed from microscopic dynamics. We show how in these systems the two timescales are in fact related. Moreover, we show that a similar connection between both scales surprisingly also exists in extremely strongly coupled systems through a phenomenon christened pole-skipping in hydrodynamic response.

Title: A CFT Distance Conjecture

Abs: We formulate conjectures relating the geometry of conformal manifolds to the spectrum of local operators in conformal field theories in d>2 spacetime dimensions. We focus on conformal manifolds with limiting points at infinite distance with respect tothe Zamolodchikov metric. Our central conjecture is that all theories at infinite distance possess an emergent higher-spin symmetry, generated by an infinite tower of currents whose anomalous dimensions vanish exponentially in the distance. Our conjecturesare related to the Distance Conjecture in the swampland program. We discuss the supporting evidence, their holographic interpretation, and implications for superconformal field theories.

Title: Replica wormhole, Page curve, global symmetry and remnant

Abstract:
A central dogma in the current theoretical study of black holes is that they can be viewed as an ordinary quantum system with large degrees of freedom. In the talk I will argue that replica wormhole gives strong evidence to the central dogma, including deriving the Page curve of the Hawking radiation, and an explicit construction of a complete basis of the black hole interior states. We will also comment on its relation with violation of global symmetry in quantum gravity.

Title: Black hole microstate statistics from Euclidean wormholes
Abstract: Over the last several years, it has been shown that black hole microstate level statistics in various models of 2D gravity are encoded in wormhole amplitudes. These statistics quantitatively agree with predictions of random matrix theory for chaotic quantum systems; this behavior is realized since the 2D theories in question are dual to matrix models. But what about black hole microstate statistics for Einstein gravity in 3D and higher spacetime dimensions, and ultimately in non-perturbative string theory? We will discuss progress in these directions. In 3D, we compute a wormhole amplitude that encodes the energy level statistics of BTZ black holes. In 4D and higher, we find analogous wormholes which appear to encode the level statistics of small black holes just above threshold. Finally, we study analogous Euclidean wormholes in the low-energy limit of type IIB string theory; we provide evidence that they encode the level statistics of small black holes just above threshold in AdS5 x S5. Remarkably, these wormholes appear to be stable in appropriate regimes, and dominate over brane-anti-brane nucleation processes in the computation of black hole microstate statistics.

Title: Defects and Anomalies in Quantum Field Theories

Abstract: I will review some recent developments in understanding the structure of anomalies in the presence of defects in CFTs. The defect insertions lead to new ‘t Hooft anomalies and conformal anomalies on the defect worldvolume. The latter give riseto defect analogs of the c-theorem (a-theorem) which establish the monotonicity of defect RG flows. With supersymmetry, the defect conformal anomalies are related to the ‘t Hooft anomalies for certain U(1) R-symmetry in a simple way, and can be determinednon-perturbatively from an algebraic procedure. In the talk I’ll mostly focus on surface defects to be concrete and comment on extensions and future directions towards the end.

Title: Hints of Gravitational Ergodicity

Abstract: Recent developments on black holes have shown that a
unitarity-compatible Page curve can be obtained from an
ensemble-averaged semi-classical approximation. In this talk, we
emphasize (1) that this peculiar manifestation of unitarity is not
specific to black holes, and (2) that it can emerge from a single
realization of an underlying unitary theory. To make things explicit,
we consider a hard sphere gas leaking slowly from a small box into a
bigger box. We reproduce the unitarity-compatible Page curve of this
system, semi-classically. Berry’s ensemble in which the eigenstates
live, plays a crucial role. The computation has structural parallels
to replica wormholes, relies crucially on ensemble averaging at each
epoch, and reveals the interplay between the multiple time-scales in
the problem. Working with the ensemble averaged state rather than the
entanglement entropy, we can also engineer an information “paradox”.
Our system provides a concrete example in which the ensemble
underlying the semi-classical Page curve is an ergodic proxy for a
time average, and not an explicit average over many theories. The
questions we address here are logically independent of the existence
of horizons, so we expect that semi-classical gravity should also be
viewed in a similar light.