Universality of high-energy absorption cross sections for black holes

TL;DR

This paper demonstrates that high-energy absorption cross sections for a broad class of black holes are universally determined by properties of null geodesics on the photon sphere, using Regge pole techniques.

Contribution

It introduces a universal description of high-energy absorption cross sections for black holes via Regge pole analysis and photon sphere properties, applicable across dimensions.

Findings

Absorption fluctuations are linked to photon sphere wave properties.

High-energy cross sections are described by geodesic characteristics.

Implications for Hawking radiation are discussed.

Abstract

We consider the absorption problem for a massless scalar field propagating in static and spherically symmetric black holes of arbitrary dimension endowed with a photon sphere. For this wide class of black holes, we show that the fluctuations of the high-energy absorption cross section are totally and very simply described from the properties (dispersion relation and damping) of the waves trapped near the photon sphere and therefore, in the eikonal regime, from the characteristics (orbital period and Lyapunov exponent) of the null unstable geodesics lying on the photon sphere. This is achieved by using Regge pole techniques. They permit us to make an elegant and powerful resummation of the absorption cross section and to extract then all the physical information encoded in the sum over the partial wave contributions. Our analysis induces moreover some consequences concerning Hawking radiation which we briefly report.