Brane cosmological perturbations

TL;DR

This paper investigates cosmological perturbations within brane cosmology, deriving equations for bulk perturbations in warped spacetimes and analyzing scalar, vector, and tensor modes with junction conditions linking brane matter to bulk geometry.

Contribution

It provides a comprehensive derivation of perturbation equations in general warped spacetimes and specializes these results to five-dimensional models, including mode decomposition and junction conditions.

Findings

Derived bulk perturbation equations for warped geometries

Decomposed perturbations into scalar, vector, and tensor modes

Computed junction conditions relating brane matter and bulk geometry

Abstract

We address the question of cosmological perturbations in the context of brane cosmology, where our Universe is a three-brane where matter is confined, whereas gravity lives in a higher dimensional spacetime. The equations governing the bulk perturbations are computed in the case of a general warped universe. The results are then specialized to the case of a five-dimensional spacetime, scenario which has recently attracted a lot of attention. In this context, we decompose the perturbations into `scalar', `vector' and `tensor' modes, which are familiar in the standard theory of cosmological perturbations. The junction conditions, which relate the metric perturbations to the matter perturbations in the brane, are then computed.