Precision Microstate Counting of Small Black Rings

TL;DR

This paper calculates the microstate degeneracy of small black rings in five-dimensional string theories, confirming exact agreement with macroscopic predictions and analyzing geometric constraints related to causality.

Contribution

It provides an exact microstate counting for small black rings using the 4D-5D connection, a novel approach in understanding their quantum structure.

Findings

Exact microstate degeneracy matches macroscopic calculations.

The Regge bound is linked to the absence of closed time-like curves.

Small black rings are related to four-dimensional non-spinning black holes.

Abstract

We examine certain two-charge supersymmetric states with spin in five-dimensional string theories which can be viewed as small black rings when the gravitational coupling is large. Using the 4D-5D connection, these small black rings correspond to four-dimensional non-spinning small black holes. Using this correspondence, we compute the degeneracy of the microstates of the small black rings exactly and show that it is in precise agreement with the macroscopic degeneracy to all orders in an asymptotic expansion. Furthermore, we analyze the five-dimensional small black ring geometry and show qualitatively that the Regge bound arises from the requirement that closed time-like curves be absent.