String-Corrected Black Holes

TL;DR

This paper explores how stringy higher curvature corrections modify four-dimensional black hole geometries, transforming singularities and altering gravitational forces, with implications for black hole causal structures and compactification effects.

Contribution

It demonstrates that string corrections change black hole singularities into horizons and modify gravitational forces, aligning the causal structure with more complex black hole solutions.

Findings

Null singularities become horizons due to string corrections.

Gravitational force can be repulsive or less attractive.

Penrose diagram matches that of four-charge black holes.

Abstract

We investigate the geometry of four dimensional black hole solutions in the presence of stringy higher curvature corrections to the low energy effective action. For certain supersymmetric two charge black holes these corrections drastically alter the causal structure of the solution, converting seemingly pathological null singularities into timelike singularities hidden behind a finite area horizon. We establish, analytically and numerically, that the string-corrected two-charge black hole metric has the same Penrose diagram as the extremal four-charge black hole. The higher derivative terms lead to another dramatic effect -- the gravitational force exerted by a black hole on an inertial observer is no longer purely attractive! The magnitude of this effect is related to the size of the compactification manifold.