HEP Theory Journal Club

Brane motion in a compact space: adiabatic perturbations of brane-bulk

Fangyi Guo

McGill

When a brane is moving in a compact space, bulk-probing signals originating at the brane can arrive back at the brane outside the light cone of the emitting event. In this work, we study how adiabatic perturbations in the brane fluid, coupled to a bulk fluid, propagate in the moving brane. In the non-dissipative regime, we find an effective sound speed for such perturbations, depending on the brane and bulk fluid energy densities, equations of state, and brane speed. In the tight-coupling approximation, the effective sound speed might be superluminal for brane and bulk fluids that satisfy the strong energy condition. This has immediate consequences for brane-world cosmology models.