Superradiant Amplification of a Scalar Wave Coupled Kinematically to Curvature Scattered off a Reissner-Nordstr\"om Black Hole

TL;DR

This paper investigates how a kinematic coupling between a massive charged scalar wave and Einstein tensor leads to superradiant amplification and instability in the spacetime of a Reissner-Nordström black hole.

Contribution

It introduces a novel kinematic coupling to Einstein tensor and demonstrates its effect on superradiant amplification and black hole instability.

Findings

Superradiant amplification increases with coupling strength.

Reissner-Nordström spacetime becomes unstable due to this coupling.

New coupling mechanism affects scalar wave dynamics near black holes.

Abstract

We study the dynamics of a massive charged scalar wave which except its canonical coupling to gravity it is also coupled kinematically to Einstein tensor. We find that as the strength of the new coupling is increased the scattered wave off the horizon of a Reissner-Nordstr\"om black hole is superradiantly amplified resulting to the instability of the Reissner-Nordstr\"om spacetime.