Solving the hierarchy problem in two-brane cosmological models - art. no. 126004

We analyze cosmological solutions in the class of two-brane models with arb itrary tensions which contain matter with general equations of state. We sh ow that the mass hierarchy between the two branes is determined by the rati o of the lapse functions evaluated on the branes. This ratio can be suffici ently small without fine-tuning the brane separation, once the transverse d imension is stabilized. For suitably large interbrane separations, both bra ne tensions are positive. We also find that the cosmological evolution obey s the standard four-dimensional Friedmann equation up to small corrections.