Complete stability for spherically symmetric backgrounds in beyond Horndeski theory

Abstract

We consider a general static, spherically symmetric background in the quadratic beyond Horndeski theory and analyse the behaviour of linear perturbations in both parity odd and parity even sectors. We derive a full set of stability conditions for an arbitrary static, spherically symmetric solution which guarantees absence of ghosts, gradient instabilities, tachyons and superluminal modes in both sectors.