Superradiance around Rotating Dilatonic Black Hole

TL;DR

This paper investigates superradiance phenomena around rotating dilatonic black holes, revealing that coupling strength influences emission rates and the nature of primordial black holes in higher-dimensional theories.

Contribution

It analyzes superradiance in dilatonic black holes for specific coupling constants, highlighting the impact of coupling on emission rates and black hole properties.

Findings

Superradiance rate increases with coupling constant beyond a critical value.

Maximally charged black holes exhibit higher emission rates than Kerr-Newman.

Primordial black holes tend to be either rotating neutral or charged non-rotating in higher dimensions.

Abstract

We consider a superradiance effect around rotating dilatonic black holes. We analyze two cases: one is an exact solution with the coupling constant $\alpha=\sqrt{3}$, which effective action is reduced from the 5-dimensional Kaluza-Klein theory, and the other is a slowly rotating dilatonic black holes with arbitrary coupling constant. We find that there exists a critical value ($\alpha \sim 1$), which is predicted from a superstring model, and the superradiant emission rate with coupling larger than the critical value becomes much higher than the Kerr-Newman case ($\alpha=0$) in the maximally charged limit. Consequently, 4-dimensional primordial black holes in higher dimensional unified theories are either rotating but almost neutral or charged but effectively non-rotating.