Black holes and stars in Horndeski theory

TL;DR

This paper reviews various black hole and star solutions within Horndeski theory, highlighting their classifications, stability, and recent developments in neutron star modeling, emphasizing the theory's rich solution landscape.

Contribution

It provides a comprehensive review of black hole and star solutions in Horndeski theory, including new classifications, stability analyses, and recent neutron star results.

Findings

Black holes involve Kaluza-Klein reduction or specific couplings in Horndeski theory.

Stable and rotating black hole solutions are identified and analyzed.

Recent neutron star solutions in Horndeski theories are discussed.

Abstract

We review black hole and star solutions for Horndeski theory. For non-shift symmetric theories, black holes involve a Kaluza-Klein reduction of higher dimensional Lovelock solutions. On the other hand, for shift symmetric theories of Horndeski and beyond Horndeski, black holes involve two classes of solutions: those that include, at the level of the action, a linear coupling to the Gauss-Bonnet term and those that involve time dependence in the galileon field. We analyze the latter class in detail for a specific subclass of Horndeski theory, discussing the general solution of a static and spherically symmetric spacetime. We then discuss stability issues, slowly rotating solutions as well as black holes coupled to matter. The latter case involves a conformally coupled scalar field as well as an electromagnetic field and the (primary) hair black holes thus obtained. We review and discuss the recent results on neutron stars in Horndeski theories.