On Cosmological Perturbations on a Brane in an Anti-de Sitter Bulk

TL;DR

This paper develops a new gauge framework to analyze cosmological perturbations on a brane within an Anti-de Sitter bulk, highlighting the role of bulk gravitons in generating anisotropies and isocurvature modes.

Contribution

It introduces a novel gauge that simplifies the five-dimensional perturbation problem and derives equations for scalar, vector, and tensor modes in this setup.

Findings

Bulk gravitons source brane perturbations.

Isocurvature modes are generated by bulk gravitons.

The new gauge facilitates solving the 5D perturbation equations.

Abstract

In this paper, we consider cosmological perturbations on a brane universe embedded in an Anti-de Sitter bulk. We use a novel gauge, in which the full five-dimensional problem is in principle solvable. In this gauge we derive the equations for scalar, vector and tensor perturbations. These equations are necessary in order to calculate microwave background anisotropies in this particular scenario. Throughout the paper, we draw attention to the influence of the bulk gravitons, which act as a source for the perturbations on the brane. In addition, we find that isocurvature modes are generated due to the influence of bulk gravitons.