A kinematical approach to Cosmic Microwave Background anisotropies

This thesis investigates the influence of gravitational perturbations on the anisotropies of the Cosmic Microwave Background (CMB) in the post-Recombination era. By systematically incorporating both first- and second-order perturbations, including scalar, vector, and tensor modes, within a flat Friedmann-Lemaˆıtre- Robertson-Walker (FLRW) Universe, the study elucidates the impact of inhomogeneities on the CMB signal. Working in the Poisson gauge and modeling Dark Energy as a Cosmological Constant, the analysis contrasts the ΛCDM scenario with the traditionally assumed Einstein–de Sitter (EdS) model. The results reveal how higher-order corrections affect the anisotropy spectrum, thereby refining our understanding of CMB observations and providing insights into the role of Dark Energy in the evolution of cosmic structures.