Quasinormal modes and Strong Cosmic Censorship

TL;DR

This paper investigates the decay of scalar perturbations around Reissner--Nordstrom--de Sitter black holes through quasinormal modes, revealing three mode families and suggesting potential violations of the strong cosmic censorship conjecture near extremality.

Contribution

It identifies and characterizes three distinct families of quasinormal modes in charged de Sitter black holes, including two previously unnoticed modes, and explores implications for cosmic censorship.

Findings

Three families of quasinormal modes identified, including two novel ones.

Decay rates of scalar fields linked to these modes influence cosmic censorship.

Potential violation of strong cosmic censorship in near-extremal black holes.

Abstract

The fate of Cauchy horizons, such as those found inside charged black holes, is intrinsically connected to the decay of small perturbations exterior to the event horizon. As such, the validity of the strong cosmic censorship (SCC) conjecture is tied to how effectively the exterior damps fluctuations. Here, we study massless scalar fields in the exterior of Reissner--Nordstrom--de Sitter black holes. Their decay rates are governed by quasinormal modes of the black hole. We identify three families of modes in these spacetimes: one directly linked to the photon sphere, well described by standard WKB-type tools; another family whose existence and timescale is closely related to the de Sitter horizon. Finally, a third family which dominates for near-extremally-charged black holes and which is also present in asymptotically flat spacetimes. The last two families of modes seem to have gone unnoticed in the literature. We give a detailed description of linear scalar perturbations of such black holes, and conjecture that SCC is violated in the near extremal regime.