Orateur
Description
Distortions of the CMB power spectrum have been proven to be a powerful probe for several cosmological and astrophysical processes. The energy distribution of the photons could provide complementary information to the well-studied temperature anisotropies, directly accessing pre-recombination physics. Each process releasing energy or changing the photon number density through the history of the Universe has left an imprint on the CMB, allowing for the possibility of putting constraints. Most previous studies focused on the monopole component only, but recently a framework has been developed that generalises the usual computation of CMB temperature and polarisation anisotropies. In our work, we used this new system of equations, implemented into the code CosmoTherm, to put limits on photon-to-dark-photon conversions. In this talk, after a brief introduction on the field, I will present this new framework and the computed transfer functions and cross-correlated power spectra. We were also able to place complementary limits on the dark photon model parameters using Planck data, finding constraints only marginally weaker than those obtained with COBE/FIRAS for the monopole distortion.