Stealth black holes in shift symmetric kinetic gravity braiding

TL;DR

This paper identifies all stealth black hole solutions within a broad class of shift symmetric scalar-tensor theories, revealing a loophole that allows such solutions without breaking shift symmetry, and discusses their properties and implications.

Contribution

It demonstrates the existence of stealth black holes in kinetic gravity braiding theories without shift symmetry breaking, using a novel approach and highlighting the role of covariantly constant kinetic density.

Findings

All stealth black holes in the theory class are derived.

A loophole in previous no-go theorems is exploited.

Stealth solutions exhibit a singular effective metric for scalar perturbations.

Abstract

We derive all hairy stealth black holes in the most general second-order, shift symmetric, scalar-tensor theory with luminally propagating gravitational waves, often called kinetic gravity braiding. Our approach exploits an overlooked loophole in a recently obtained no-go statement which claims shift symmetry breaking to be necessary for stealth solutions to exist in kinetic gravity braiding. We highlight the essential role played by a covariantly constant kinetic density in obtaining these solutions. Lastly, we propose a parametrization of the theories based on the asymptotics of its stealth solutions and comment on the intriguing singular effective metric for scalar perturbations in stealth black holes.