Non-conventional cosmology from a brane-universe

TL;DR

The paper shows that a universe confined to a 3-brane in a five-dimensional spacetime exhibits cosmology that deviates from standard Friedmann dynamics, with a quadratic dependence of the Hubble rate on the brane energy density and no direct appearance of the four-dimensional Newton constant. Using the Gauss-Codazzi formalism and Israel junction conditions, the authors derive the brane cosmology and construct exact global solutions with a constant 5D radius, illustrating how brane and bulk matter are topologically coupled. They show that global (multi-brane) configurations are required for consistency on a compact extra dimension and discuss how a Kaluza-Klein reduction can reproduce the same non-standard dynamics when topological constraints are included. The work explores the cosmological consequences, including nucleosynthesis constraints and implications for inflation, and outlines directions for extensions to more dimensions and perturbations. The results provide a concrete demonstration that brane-world cosmology can yield qualitatively different early- and late-time dynamics, with potential observational tests in high-energy and gravitational phenomena.

Abstract

We consider ``brane-universes'', where matter is confined to four-dimensional hypersurfaces (three-branes) whereas one extra compact dimension is felt by gravity only. We show that the cosmology of such branes is definitely different from standard cosmology and identify the reasons behind this difference. We give a new class of exact solutions with a constant five-dimensional radius and cosmologically evolving brane. We discuss various consequences.