Destabilization of black holes and stars by generalized Proca fields

TL;DR

This paper shows that black holes and stars can become unstable due to non-minimally coupled vector fields in certain theories, impacting models of dark energy and dark matter.

Contribution

It identifies conditions under which generalized Proca fields cause instabilities in astrophysical objects, extending understanding of their role in cosmology.

Findings

Black holes with small mass are unstable under certain vector field perturbations.

High-density stars can experience ghost or gradient instabilities due to non-minimal couplings.

Stability bounds are relevant for dark energy and ultra-light dark matter models.

Abstract

We demonstrate that black holes and stars in general relativity can be destabilized by perturbations of non-minimally coupled vector fields. Focusing on static and spherically symmetric backgrounds, our analysis shows that black holes with sufficiently small mass and stars with sufficiently high densities are subject to ghost or gradient-type instabilities. This holds for a large class of vector-tensor theories whenever non-minimal couplings contribute to linearized dynamics about a state with vanishing vector field and applies to generalized Proca models that have sparked attention for their potential role in cosmology and astrophysics. The stability criteria translate into bounds of relevance for low-scale theories of dark energy and for ultra-light dark matter scenarios.