Quasinormal modes and a new instability of Einstein-Gauss-Bonnet black holes in the de Sitter world

TL;DR

This paper discovers a new dynamical instability in Einstein-Gauss-Bonnet black holes within a de Sitter universe, driven by the cosmological constant, and analyzes their quasinormal modes and stability properties.

Contribution

It identifies a novel instability specific to de Sitter Einstein-Gauss-Bonnet black holes and examines the quasinormal spectrum's compliance with Hod's bound across different perturbation types.

Findings

New instability in scalar gravitational perturbations due to cosmological constant

Vector and tensor perturbations obey Hod's bound

Scalar perturbations do not obey Hod's bound

Abstract

Analysis of time-domain profiles for gravitational perturbations shows that Gauss-Bonnet black holes in a de Sitter world possess a new kind of dynamical instability which does not take place for asymptotically flat Einstein-Gauss-Bonnet black holes. The new instability is in the gravitational perturbations of the scalar type and is due to the nonvanishing cosmological constant. Analysis of the quasinormal spectrum in the stability sector shows that although the scalar type of gravitational perturbations alone does not obey Hod's conjectural bound, connecting the damping rate and the Hawking temperature, the vector and tensor types (and thereby the gravitational spectrum as a whole) do obey it.