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

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.