A Stringy Cloak for a Classical Singularity

TL;DR

The paper shows that higher-derivative corrections from string theory can cloak classical null singularities of certain Calabi–Yau black holes, producing regular black holes with AdS2×S2 horizons and finite area. Using 4D N=2 supergravity with an ${\hat{A}}$-dependent prepotential and the generalized attractor mechanism, the authors derive corrected entropy formulas via Wald's construction and identify cases where the entropy deviates from the canonical $S=A/4$ relation. For Calabi–Yau black holes with vanishing classical area, quantum corrections yield a horizon area and an entropy related by $S = A/2$, with explicit realizations in two-charge configurations on $K_3\times T^2$ that match microscopic degeneracy and dual D1–D5 descriptions. The results illustrate a concrete stringy mechanism for resolving classical singularities and suggest avenues for extending attractor/OSV analyses to other zero-area solutions and higher-order corrections.

Abstract

We consider a class of 4D supersymmetric black hole solutions, arising from string theory compactifications, which classically have vanishing horizon area and singular space-time geometry. String theory motivates the inclusion of higher derivative terms, which convert these singular classical solutions into regular black holes with finite horizon area. In particular, the supersymmetric attractor equations imply that the central charge, which determines the radius of the $AdS_2\times S^2$ near horizon geometry, acquires a non-vanishing value due to quantum effects. In this case quantum corrections to the Bekenstein-Hawking relation between entropy and area are large. This is the first explicit example where stringy quantum gravity effects replace a classical null singularity by a black hole with finite horizon area.