CMB Anisotropies and Theories of the Early Universe

I present recent work aimed at showing how currently competing theories of the early universe leave their imprint on the temperature anisotropies of the CMB radiation. We consider the 3-point correlation function, as well as the inherent theoretical uncertainties associated with it, for which we derive explicit analytic formulae. We apply them in the study of non-Gaussian features that arise on large scales in the framework of both inflationary and topological defects models. For inflation, we develop a perturbative analysis for the study of spatial correlations in the inflaton in the context of the stochastic approach to inflation. We also include an analysis of a particular geometry, the so-called `collapsed' 3-point function, in the case of post recombination integrated effects, arising generically whenever the mildly non linear growth of perturbations is taken into account. We also devote a part of the thesis to the study of recently proposed analytic models of topological defects, and implement them in the analysis of both the CMB excess kurtosis (for cosmic strings) and the CMB collapsed 3-point function and skewness (for textures). Lastly, we present a study of the CMB anisotropies on the degree angular scale in the framework of the global texture scenario, and show the relevant features that arise; among these, the Doppler peaks.