Absorption of photons and fermions by black holes in four dimensions

TL;DR

This paper analyzes how photons and fermions are absorbed by four-dimensional black holes, deriving absorption cross-sections that align with effective string models and proposing a supersymmetry-respecting coupling for supergravity fields.

Contribution

It introduces a method to compute absorption cross-sections for black holes using dyadic index techniques and proposes a supersymmetric coupling model consistent with supergravity.

Findings

Absorption cross-sections match effective string model predictions at low energies.

Coupling to the effective string respects supersymmetry and predicts cross-sections for various fields.

Results support the effective string description of black hole absorption phenomena.

Abstract

The absorption of photons and fermions into four-dimensional black holes is described by equations which in certain cases can be analyzed using dyadic index techniques. The resulting absorption cross-sections for near-extremal black holes have a form at low energies suggestive of the effective string model. A coupling to the effective string is proposed for spin-0 and spin-1/2 fields of pure N=4 supergravity which respects the unbroken supersymmetry of extreme black holes and correctly predicts dilaton, axion, and fermion cross-sections up to an overall normalization.