Are braneworlds born isotropic?

Dunsby, Peter K S; Goheer, Naureen; Bruni, Marco; Coley, Alan

Are braneworlds born isotropic?

Journal Article

2004

Journal Title

Physical Review D - Particles and Fields

Link to Journal

https://dx.doi.org/10.1103/PhysRevD.69.101303

Department

Department of Mathematics and Applied Mathematics

Faculty

Faculty of Science

Abstract

It has recently been suggested that an isotropic singularity may be a generic feature of brane cosmologies, even in the inhomogeneous case. Using the covariant and gauge-invariant approach we present a detailed analysis of linear perturbations of the isotropic model ${cal F}_b$ which is a past attractor in the phase space of homogeneous Bianchi models on the brane. We find that for matter with an equation of state parameter $gamma > 1$, the dimensionless variables representing generic anisotropic and inhomogeneous perturbations decay as $tto 0$, showing that the model ${cal F}_b$ is asymptotically stable in the past. We conclude that brane universes are born with isotropy naturally built-in, contrary to standard cosmology. The observed large-scale homogeneity and isotropy of the universe can therefore be explained as a consequence of the initial conditions if the brane-world paradigm represents a description of the very early universe. Comment: Changed to match published version