P. Peter: Post-doctoral position at the Department of Applied Mathematics and Theoretical Physics (DAMTP), Cambridge University. Research positions: Chargé de Recherches (1994-2002), Medaille de bronze (bronze medal) du CNRS (1995), Directeur de Recherches, Institut d'Astrophysique de Paris since 2002.; J.P. Uzan: Post-doctoral position at the Department of Theoretical Physics (DPT), Geneva University. Research positions: Chargé de Rechecherches au CNR, teaches the course of Theoretical Cosmology at the Ecole Normale Supérieure, teaches at the Ecole Nationale Supérieure des Mines de Paris.