Black Hole Greybody Factors and Absorption of Scalars by Effective Strings

TL;DR

This paper calculates greybody factors for charged black holes and compares them with predictions from an effective string model, finding good agreement in certain regimes and suggesting possible model improvements.

Contribution

It provides a detailed comparison of black hole greybody factors with an effective string model, highlighting regimes of agreement and areas for refinement.

Findings

Greybody factors match effective string predictions at low temperatures.

Agreement is only at leading order when temperatures are high.

Relations suggest potential modifications to the effective string model.

Abstract

We compute the greybody factors for classical black holes in a domain where two kinds of charges and their anticharges are excited by the extra energy over extremality. We compare the result to the greybody factors expected from an effective string model which was earlier shown to give the correct entropy. In the regime where the left and right moving temperatures are much smaller than the square root of the effective string tension, we find a non-trivial greybody factor which agrees with the effective string model. However, if the temperatures are comparable with the square root of the effective string tension, the greybody factors agree only at the leading order in energy. Nevertheless, there are several interesting relations between the two results, suggesting that a modification of the effective string model might lead to better agreement.