New Gauss-Bonnet black holes with curvature induced scalarization in the extended scalar-tensor theories

TL;DR

This paper introduces new black hole solutions in extended scalar-tensor-Gauss-Bonnet theories, where scalarization occurs in high curvature regimes, leading to stable and unstable branches of scalarized black holes similar to neutron star scalarization.

Contribution

The paper demonstrates the existence of curvature-induced scalarized black holes in ESTGB theories, expanding understanding of black hole solutions with scalar fields in high curvature regimes.

Findings

Existence of new scalarized black hole solutions

Bifurcation of solutions at certain mass thresholds

Stability of the first scalarized branch

Abstract

In the present paper we consider a class of extended scalar-tensor-Gauss-Bonnet (ESTGB) theories for which the scalar degree of freedom is excited only in the extreme curvature regime. We show that in the mentioned class of ESTGB theories there exist new black hole solutions which are formed by spontaneous scalarization of the Schwarzaschild balck holes in the extreme curvature regime. In this regime, below certain mass, the Schwarzschild solution becomes unstable and new branch of solutions with nontrivial scalar field bifurcate from the Schwarzschild one. As a matter of fact, more than one branches with nontrivial scalar field can bifurcate at different masses but only the first one is supposed to be stable. This effect is quite similar to the spontaneous scalarization of neutron stars. In contrast with the standard spontaneous scalarization of neutron stars which is induced by the presence of matter, in our case the scalarization is induced by the curvature of the spacetime.