Cosmological matching conditions and galilean genesis in Horndeski's theory

Understand

We derive the cosmological matching conditions for the homogeneous and isotropic background and for linear perturbations in Horndeski's most general second-order scalar-tensor theory.

• In general relativity, the matching is done in such a way that the extrinsic curvature is continuous across the transition hypersurface.
• This procedure is generalized so as to incorporate the mixing of scalar and gravity kinetic terms in the field equations of Horndeski's theory.
• Our matching conditions have a wide range of applications including the galilean genesis and the bounce scenarios, in which stable, null energy condition violating solutions play a central role.