Stealth black holes in shift symmetric kinetic gravity braiding

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.