1+3 Covariant Cosmic Microwave Background anisotropies II: The almost - Friedmann Lemaitre model

Abstract

This is the second of a series of papers extending the 1+3 covariant and gauge invariant treatment of kinetic theory to an examination of Cosmic Microwave Background temperature anisotropies arising from inhomogeneities in the early universe. The first paper dealt with algebraic issues. Here we derive the mode form of the integrated Boltzmann equations, first, giving a covariant version of the standard derivation using the mode recursion relations, second, demonstrating the link to the multipole divergence equations and finally various analytic ways of solving the resulting equations are discussed. A general integral form of solution is obtained for the equations with Thomson scattering. The covariant Friedmann-Lemaitre multipole form of the transport equations are found using the covariant and gauge-invariant generalization of the Peebles and Yu expansion in Thompson scattering time. The dispersion relations and damping scale are then obtained from the covariant approach. The equations are integrated to give the covariant and gauge-invariant equivalent of the canonical scalar sourced anisotropies. We carry out a simple treatment of the matter dominated free-streaming projection, slow decoupling, and tight-coupling cases, with the aim both giving a unified transparent derivation of this range of results and clarifying the connection between the more usual approaches (for example that of Hu and Sugiyama) and the treatment for scalar perturbations (for example the treatment of Challinor and Lasenby).