Reissner-Nordstr\"om black holes in de Sitter space-time: bounds with quasinormal frequencies

TL;DR

This paper investigates the quasinormal modes of charged scalar fields around Reissner-Nordström-de Sitter black holes, revealing potential violations of Strong Cosmic Censorship near extremality due to bounds from the Weak Gravity Conjecture and Festina-Lente.

Contribution

It provides a semi-classical analysis linking quasinormal modes with cosmic censorship and quantum gravity bounds in charged de Sitter black holes.

Findings

Modes become unstable near extremality with positive cosmological constant

Strong Cosmic Censorship may be violated close to extremal conditions

Bounds from WGC and FL influence the stability and structure of black holes

Abstract

Rich physics can be divined from charged black holes subjected to extremal conditions. When applied in conjunction with principles like Weak Cosmic Censorship, this naturally leads to constraints on the mass and charge of the black hole. However, more nuanced principles such as the Weak Gravity Conjecture (WGC) and the recently proposed Festina-Lente (FL) bound can provide, respectively, upper and lower bounds on elementary charged particles. In this study, we examine the quasinormal modes (QNMs) exhibited by a massive scalar test field carrying an electric charge, oscillating in the outer region of the black hole. These modes are subjected to the constraints imposed by the FL and WGC bounds. Our analysis provides insight into the behaviour of QNMs, particularly in regions that approach the extremal conditions of the black hole. Notably, in these regimes, the stability of the modes becomes precarious, particularly in the presence of a positive cosmological constant. The implications of our findings are far-reaching and significant. They extend from safeguarding the principles of cosmic censorship to addressing the structural stability of the black hole's interior. Our semi-classical analysis presents compelling evidence suggesting that Strong Cosmic Censorship may be violated for black holes that are in close proximity to extremality within the context of Reissner-Nordstr\"om-de Sitter (RNdS) geometries.