Instability of charged massive scalar fields in bound states around Kerr-Sen black holes

TL;DR

This paper demonstrates that charged massive scalar fields in bound states around Kerr-Sen black holes are unstable due to an amplification effect, identified through analytical solution matching of the Klein-Gordon equation.

Contribution

It provides the first analytical proof of instability for charged massive scalar fields in Kerr-Sen black hole backgrounds by matching near and far region solutions.

Findings

Charged massive scalar fields exhibit instability around Kerr-Sen black holes.

Bound state frequencies have an imaginary component indicating growth.

The instability is analytically demonstrated through solution matching.

Abstract

We show the instability of a charged massive scalar field in bound states around Kerr-Sen black holes. By matching the near and far region solutions of the radial part in the corresponding Klein-Gordon equation, one can show that the frequency of bound state scalar fields contains an imaginary component which gives rise to an amplification factor for the fields. Hence, the unstable modes for a charged and massive scalar perturbation in Kerr-Sen background can be shown.