On junction conditions in gravity theories with higher curvature terms

Abstract

We discuss the junction conditions in the context of the Randall-Sundrum model with the Gauss-Bonnet interaction. We consider the $Z_2$ symmetric model where the brane is embedded in an $AdS_5$ bulk, as well as a model without $Z_2$ symmetry in which the brane (in this case called by tradition ``shell'') separates two metrically different $AdS_5$ regions. We show that the Israel junction conditions across the membrane (that is either a brane or a shell) have to be modified if more general equations than Einstein's, including higher curvature terms, hold in the bulk, as is likely to be the case in a low energy limit of string theory. We find that the membrane can then no longer be treated in the thin wall approximation. We derive the junction conditions for the Einstein-Gauss-Bonnet theory including second order curvature terms and show that the microphysics of Gauss-Bonnet thick membranes may, in some instances, be simply hidden in a renormalization of Einstein's constant.