Cosmological perturbations of an expanding brane in an anti-de Sitter bulk: a short review

TL;DR

This review discusses the study of cosmological perturbations in an expanding brane within an anti-de Sitter bulk, highlighting the challenges in connecting brane and bulk perspectives for making predictions.

Contribution

It summarizes the current understanding of perturbations in brane cosmology and emphasizes the unresolved issues in linking brane and bulk viewpoints.

Findings

Identifies a gap between brane and bulk perspectives in perturbation analysis.

Highlights the complexity of predicting observable signatures in brane-world models.

Notes the need for further research to connect theoretical models with cosmological observations.

Abstract

Since the Randall-Sundrum 1999 papers, braneworlds have been a favourite playground to test string inspired cosmological models. The subject has developped into two main directions : elaborating more complex models in order to strenghten the connection with string theories, and trying to confront them with observations, in particular the Cosmic Microwave Background anisotropies. We review here the latter and see that, even in the simple, "paradigmatic", case of a single expanding brane in a 5D anti-de Sitter bulk, there is still a missing link between the "view from the brane" and the "view from the bulk" which prevents definite predictions.