Bifurcation of the quasinormal spectrum and Zero Damped Modes for rotating dilatonic black holes

TL;DR

This paper demonstrates that Zero Damped Modes and quasinormal mode bifurcation, previously observed in Kerr black holes, also occur in rotating dilatonic black holes, and clarifies the stability of charged scalar fields in this context.

Contribution

It extends the understanding of quasinormal mode bifurcation and Zero Damped Modes to rotating dilatonic black holes, providing both numerical and analytical results.

Findings

Zero Damped Modes found in rotating dilatonic black holes

No instability of charged massive scalar fields under proper boundary conditions

Analytic quasinormal frequency expressions derived for large coupling regimes

Abstract

It has been recently found that for the near extremal Kerr black holes appearing of Zero Damped Modes (accompanied by qusinormal mode branching) signifies about inapplicability of the regime of small perturbations and the onset of turbulence. Here we show that this phenomena is not limited by Kerr or Kerr-Newman solutions only, but also takes place for rotating dilatonic black holes for which we have found Zero Damped Modes both numerically and analytically. We have also shown that, contrary to recent claims, there is no instability of a charged massive scalar field in the background of the rotating dilatonic black hole under physically adequate boundary conditions. Analytic expression for dominant quasinormal frequencies is deduced in the regime of large coupling qQ, where q and Q are the field and black hole charges respectively.