The small black hole illusion

TL;DR

This paper challenges the idea that higher-curvature corrections resolve the singular horizons of small black holes in string theory, highlighting the role of solitonic 5-branes and Kaluza-Klein monopoles in their microscopic structure.

Contribution

It critically examines the resolution of small black hole singularities, emphasizing the importance of correctly identifying fundamental constituents in the presence of higher-curvature interactions.

Findings

Quadratic curvature corrections do not resolve the singular horizon.

The reported resolution involves solitonic 5-branes with screened charges.

Kaluza-Klein monopoles retain their charge, affecting the black hole's microscopic description.

Abstract

Small black holes in string theory are characterized by a classically singular horizon with vanishing Bekenstein-Hawking entropy. It has been argued that higher-curvature corrections resolve the horizon and that the associated Wald entropy is in agreement with the microscopic degeneracy. In this note we study the heterotic two-charge small black hole and question this result, which we claim is caused by a misidentification of the fundamental constituents of the system studied when higher-curvature interactions are present. On the one hand, we show that quadratic curvature corrections do not solve the singular horizon of small black holes. On the other, we argue that the resolution of the heterotic small black hole reported in the literature involves the introduction of solitonic 5-branes, whose asymptotic charge vanishes due to a screening effect induced by the higher-curvature interactions, and a Kaluza-Klein monopole, whose charge remains unscreened.