General Rotating Black Holes in String Theory: Greybody Factors and Event Horizons

TL;DR

This paper derives the wave equation for scalar fields in five-dimensional rotating black holes, models their microscopic structure via effective string theory, and calculates greybody factors to understand Hawking radiation microscopically.

Contribution

It generalizes wave equations to rotating black holes, introduces a U-duality invariant effective string length, and refines the understanding of Hawking emission spectra in this context.

Findings

Derived wave equation for rotating black holes

Calculated greybody factors and Hawking spectra

Proposed a U-duality invariant effective string length

Abstract

We derive the wave equation for a minimally coupled scalar field in the background of a general rotating five-dimensional black hole. It is written in a form that involves two types of thermodynamic variables, defined at the inner and outer event horizon, respectively. We model the microscopic structure as an effective string theory, with the thermodynamic properties of the left and right moving excitations related to those of the horizons. Previously known solutions to the wave equation are generalized to the rotating case, and their regime of validity is sharpened. We calculate the greybody factors and interpret the resulting Hawking emission spectrum microscopically in several limits. We find a U-duality invariant expression for the effective string length that does not assume a hierarchy between the charges. It accounts for the universal low-energy absorption cross-section in the general non-extremal case.