A massive charged scalar field in the Kerr-Newman background I: quasinormal modes, late-time tails and stability

TL;DR

This paper provides a comprehensive analysis of quasinormal modes, late-time tails, and stability of a massive charged scalar field around Kerr-Newman black holes across all relevant parameters, showing no instability despite superradiance effects.

Contribution

It offers the first complete characterization of quasinormal modes and late-time tails for massive charged scalar fields in Kerr-Newman backgrounds for all parameter ranges, including analytic formulas and mode branching.

Findings

No instability observed under quasinormal mode boundary conditions.

Analytic formulas derived for large qQ regime.

Asymptotic tails dominate for highly charged fields.

Abstract

So far analysis of the quasinormal spectrum of a massive charged scalar field in the black hole background has been limited by the regime of small \mu M and qQ, where \mu, q (M, Q) are mass and charge of the field (black hole). Here we shall present a comprehensive picture of quasinormal modes, late-time tails and stability of a massive charged scalar field around Kerr-Newman black holes for any physically meaningful values of the parameters. We shall show that despite presence of the two mechanisms of superradiance (owing to black hole's rotation and charge) and the massive term creating growing bound states, there is no indication of instability under quasinormal modes' boundary conditions. We have shown that for some moderate values of qQ dominant quasinormal modes may have arbitrarily small real oscillation frequencies Re(\omega). An analytic formula for the quasinormal modes has been derived in the regime of large qQ. The larger the field's charge, the sooner asymptotic tails dominate in a signal, making it difficult to extract quasinormal frequencies from a time-domain profile. Analytic expressions for intermediate and asymptotically late-time tails have been found for the Reissner-Nordstr\"om black hole. For the near extremal Kerr-Newman black holes we have obtained a more general picture of the mode branching found recently for massless fields [arXiv:1212.3271] in the Kerr background.