Mon, Oct 5, 2020, 12:30 pm
A basic challenge for any theory of quantum gravity is to provide a microscopic accounting of the degrees of freedom and partition functions of black holes. In string theory, an exact count is possible when the Hawking temperature T=0, which corresponds to extremal Reissner-Nordstrom black holes BPS protected by supersymmetry. What happens for T>0 is less clear, including whether there is a mass gap separating extremal and non-extremal states.
Extremal black holes have an AdS2 region, and substantial progress in the last few years has been made on Jackiw-Teitelboim (JT) dilaton gravity, which is an effective theory of nearly AdS2 spacetimes appropriate for low T>0. It has been shown that JT is, in some sense, exactly solvable using an AdS/CFT dual boundary theory known as the Schwarzian.
In this talk, we will extend the AdS2 JT dynamics to the case appropriate for four-dimensional near-BPS black holes. Starting with 4D N=2 supergravity, we consider nearly AdS2 x S2 black holes with enhanced N=4 superconformal isometries. The effective description is a 2D N=4 supersymmetric extension of JT gravity dual to a supersymmetric Schwarzian. The density of near-BPS states may be computed exactly in this theory. Our results agree with general arguments from string theory and JT gravity, and we find the supersymmetry leads to a mass gap above extremality.