# Black Holes and Hurwitz Class Numbers

## TL;DR

This paper links BPS black hole counting in string theory compactified on K3×T^2 to a specific mock modular form, revealing deep connections between physics and number theory.

## Contribution

It introduces a natural counting function for black holes that is identified with Zagier's weight 3/2 mock modular form, highlighting a novel intersection of string theory and modular forms.

## Key findings

- Counting function matches Zagier's mock modular form
- Suggests profound links between black holes and number theory
- Hints at new mathematical structures in string theory

## Abstract

We define a natural counting function for BPS black holes in $K3 \times T^2$ compactification of type II string theory, and observe that it is given by a weight 3/2 mock modular form discovered by Zagier. This hints at tantalizing relations connecting black holes, string theory, and number theory.