Cosmic acceleration from asymmetric branes

We consider a single 3-brane sitting in between two different five dimensional spacetimes. On each side of the brane, the bulk is a solution to GaussBonnet gravity, although the bare cosmological constant, fundamental Planck scale, and Gauss-Bonnet coupling can differ. This asymmetry leads to weighted junction conditions across the brane and interesting brane cosmology. We focus on two special cases: a generalized Randall-Sundrum model without any Gauss-Bonnet terms, and a stringy model, without any bare cosmological constants, and positive Gauss-Bonnet coupling. Even though we assume there is no vacuum energy on the brane, we find late time de Sitter cosmologies can occur. Remarkably, in certain parameter regions, this acceleration is preceded by a period of matter/radiation domination, with H2 ∝ ρ, all the way back to nucleosynthesis. ∗[email protected]