[HEG] BPS Black Holes in AdS3xS3xS3xS1 and Beyond

Who: Matthew Heydeman (Harvard University)
Title: BPS Black Holes in AdS3xS3xS3xS1 and Beyond
Abstract: 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, recent progress has shown that a more careful treatment of the bulk path integral can lead to large modifications from the predictions of purely semi-classical gravity, even for supersymmetric black holes. This can lead to situations in which neither the supersymmetric index nor the Hawking area formula can correctly account for the physical degeneracies. Using the Schwarzian description in supergravity, 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. The index, while protected, necessarily misses crucial information about even the BPS spectrum.