Null shells in kinetic gravity braiding scalar-tensor theories

We derive the equation of motion of null shells generated by distributional sources with support on the shell in a class of second-order scalar-tensor theories that is both compatible with gravitational wave observations and produce valid cosmological evolution.The shell equation of motions and thus the junction conditions required for smooth matching along a null hypersurface are obtained by considering a 2+1+1 decomposition given by the null generators of the hypersurface and an auxiliary null vector field. The equations relate jumps of geometric quantities to the components of the distributional sources and also provide a constraint relation on the source components