Extremal Black Holes As Fundamental Strings

TL;DR

This paper demonstrates that polarization-dependent string scattering supports the identification of extremal black holes with fundamental heterotic strings, providing new insights into black hole entropy and string theory correspondence.

Contribution

It constructs excited heterotic string solutions with specific supersymmetry properties and matches their scattering amplitudes with string theory predictions, linking black holes to fundamental strings.

Findings

Constructed excited heterotic string solutions with arbitrary left-moving waves.

Developed methods to compute polarization-dependent scattering amplitudes beyond metric approximation.

Found perfect agreement between scattering amplitudes and heterotic string tree-level predictions.

Abstract

We show that polarization dependent string-string scattering provides new evidence for the identification of the Dabholkar-Harvey (DH) string solution with the heterotic string itself. First, we construct excited versions of the DH solution which carry arbitrary left-moving waves yet are annihilated by half the supersymmetries. These solutions correspond in a natural way to Bogomolny-bound-saturating excitations of the ground state of the heterotic string. When the excited string solutions are compactified to four dimensions, they reduce to Sen's family of extremal black hole solutions of the toroidally compactified heterotic string. We then study the large impact parameter scattering of two such string solutions. We develop methods which go beyond the metric on moduli space approximation and allow us to read off the subleading polarization dependent scattering amplitudes. We find perfect agreement with heterotic string tree amplitude predictions for the scattering of corresponding string states. Taken together, these results clearly identify the string states responsible for Sen's extremal black hole entropy. We end with a brief discussion of implications for the black hole information problem.