Instability of vectorized stars

TL;DR

This paper investigates the stability of vectorized compact objects in gravity theories, revealing that they are plagued by ghosts and instabilities, and are not stable end states as previously hoped.

Contribution

It develops tools to analyze perturbations of vectorized objects and demonstrates their inherent instabilities, contrasting with scalarized solutions.

Findings

Vectorized compact objects suffer from ghosts.

They exhibit gradient instabilities.

They are not stable end points of the instability process.

Abstract

In recent papers it has been shown that a large class of vectorization mechanisms in gravity, which involve the vector fields becoming apparently tachyonic in some regime, are actually dominated by ghosts and non-perturbative behavior. Despite this, vectorized compact object solutions have previously been found, which raises the question of how, and if, the newly discovered ghosts are quenched in these cases. Here we develop the tools to study the perturbations of vectorized compact objects, and demonstrate that they suffer from ghosts and gradient instabilities as well. Thus, these vectorized objects do not represent the stable end point of a quenched instability unlike their scalarized counterparts in the spontaneous scalarization literature.