Absorption of scalars by extremal black holes in string theory

TL;DR

This paper investigates how the low frequency absorption cross section of scalar fields by extremal black holes relates to the horizon area and entropy, especially considering string theory corrections, revealing that classical relations often do not hold with higher derivative effects.

Contribution

It demonstrates that the classical relation between absorption cross section and entropy does not generally hold when string-theoretic ' corrections are included, across various black hole configurations.

Findings

Absorption cross section equals horizon area even with ' corrections.

The classical relation  G S is generally invalid with string corrections.

The relation holds for specific supersymmetric black holes in five dimensions.

Abstract

We show that the low frequency absorption cross section of minimally coupled test massless scalar fields by extremal spherically symmetric black holes in d dimensions is equal to the horizon area, even in the presence of string--theoretical $\alpha'$ corrections. Classically one has the relation $\sigma = 4 G S$ between that absorption cross section and the black hole entropy. By comparing in each case the values of the horizon area and Wald's entropy, we discuss the validity of such relation in the presence of higher derivative corrections for extremal black holes in many different contexts: in the presence of electric and magnetic charges, for nonsupersymmetric and supersymmetric black holes, in d=4 and d=5 dimensions. The examples we consider seem to indicate that this relation is not verified in the presence of $\alpha'$ corrections in general, although being valid in some specific cases (electrically charged maximally supersymmetric black holes in d=5). We argue that the relation $\sigma = 4 G S$ should in general be valid for the absorption cross section of scalar fields which, although being independent from the black hole solution, have their origin from string theory, and therefore are not minimally coupled.