Magnetized initial conditions for CMB anisotropies

This paper introduces a systematic treatment of the linear theory of scalar gravitational perturbations in the presence of a fully inhomogeneous magnetic field. The analysis is conducted both in the synchronous and in the conformally Newtonian gauges. The cosmological plasma is assumed to be composed of cold dark matter, baryons, photons, neutrinos. The problem of superhorizon initial conditions for the fluid variables of the various species and for the coupled system of Boltzmann-Einstein equations is discussed in the presence of an inhomogeneous magnetic field. The tight-coupling approximation for the Boltzmann hierarchy is extended to the case where gravitating magnetic fields are included.