Black hole scalarization with Gauss-Bonnet and Ricci scalar couplings

TL;DR

This paper investigates how combining Gauss-Bonnet and Ricci scalar couplings influences black hole scalarization, revealing that Ricci coupling significantly affects solution properties and broadens the understanding of scalarized black holes.

Contribution

It introduces a comprehensive analysis of combined curvature couplings on black hole scalarization, highlighting the importance of Ricci coupling in solution characteristics and domain of existence.

Findings

Ricci coupling significantly alters scalarized black hole properties

Combined couplings expand the domain of scalarized solutions

Models can evade binary pulsar constraints while predicting observable deviations

Abstract

Spontaneous scalarization is a gravitational phenomenon in which deviations from general relativity arise once a certain threshold in curvature is exceeded, while being entirely absent below that threshold. For black holes, scalarization is known to be triggered by a coupling between a scalar and the Gauss-Bonnet invariant. A coupling with the Ricci scalar, which can trigger scalarization in neutron stars, is instead known to not contribute to the onset of black hole scalarization, and has so far been largely ignored in the literature when studying scalarized black holes. In this paper, we study the combined effect of both these couplings on black hole scalarization. We show that the Ricci coupling plays a significant role in the properties of scalarized solutions and their domain of existence. This work is an important step in the construction of scalarization models that evade binary pulsar constraints and have general relativity as a cosmological late-time attractor, while still predicting deviations from general relativity in black hole observations.