Cosmic acceleration from asymmetric branes

TL;DR

This paper explores how asymmetric five-dimensional spacetimes with Gauss-Bonnet gravity can induce late-time cosmic acceleration on a brane without vacuum energy, showing possible matter-dominated early universe and de Sitter late universe.

Contribution

It introduces models with asymmetric bulk spacetimes leading to brane cosmology that can produce late-time acceleration without vacuum energy, extending previous symmetric brane-world scenarios.

Findings

Late-time de Sitter cosmology can arise without brane vacuum energy.

The model allows a matter/radiation dominated era preceding acceleration.

Acceleration occurs in certain parameter regimes with different bulk properties.

Abstract

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 Gauss-Bonnet gravity, although the bare cosmological constant, funda mental 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 $H^2 \propto \rho$, all the way back to nucleosynthesis.