Charged scalar and Dirac perturbations on a global monopole Reissner-Nordstr\"om-de Sitter black hole: quasinormal modes and strong cosmic censorship

TL;DR

This paper investigates charged scalar and Dirac perturbations on a global monopole Reissner-Nordström-de Sitter black hole, analyzing quasinormal modes and implications for strong cosmic censorship using the Heun function method.

Contribution

It introduces a unified approach to compute quasinormal spectra via the Heun function method and explores the effects of a global monopole on cosmic censorship violations.

Findings

Global monopole shifts the multipole number affecting spectra.

Monopole does not affect strong cosmic censorship for scalar perturbations.

Monopole enhances violations of cosmic censorship for Dirac perturbations.

Abstract

We study perturbations of charged scalar and Dirac fields around Reissner-Nordstr\"om-de Sitter black holes with a global monopole. To this end, we first derive the equations of motion for both fields on the aforementioned background; these equations are then reformulated uniformly into the Teukolsky equation. Since the Teukolsky equation in asymptotically de Sitter spacetimes can be mapped into the Heun equation, we are able to solve quasinormal spectra by employing the Heun function method, not only for photon sphere modes but also for de Sitter and near-extremal modes. We analyze the spectra of all three types for both fields and, in particular, ascertain the effects of the global monopole. In the near-extremal regime, we find that the presence of a global monopole, on the one hand, leaves the strong cosmic censorship conjecture unaffected for scalar perturbations, while on the other hand, it enhance the violation of strong cosmic censorship for Dirac perturbations. Furthermore, we identify that the impact of the global monopole on both the spectra and the strong cosmic censorship is achieved by a shift in the modified multipole number. Our work demonstrates that the Heun function method is an efficient and robust approach for exploring the interaction between asymptotically de Sitter black holes and perturbing fields.