A complete analysis of primordial non-Gaussianity from cosmic decoherence

This thesis will be focused on the study of the problem of the classicalization of the perturbed Universe during its early stages. The quantum-to-classical problem has been widely treated in theoretical physics, and different models have been proposed. In this work we will adopt the quantum decoherence framework and apply it in a cosmological setting. In particular we will analyze the decoherence of inflationary perturbations that might leave specific observational fingerprints that could prove and/or bound their quantum nature. These fingerprints consist on a correction to the standard unitary evolution of the curvature spectra of the slow roll inflaton fluctuations. The corrections arise due to the requirement of decoherence to take place once the system (being represented by the inflating modes) interacts with an environment. By opening the system we break the unitary dynamics and a new term appears in the evolution equation for our statistical observables called Lindblad equation. In a previous work, this equation has been solved analytically and it has been found that decoherence induces a non-vanishing correction to the curvature power spectrum and to the trispectrum, but surprisingly it seemingly has no consequences on the bispectrum. However, in a more recent article, a generalized form of the pointer observable has been adopted, and it has been proven that decoherence indeed can lead to a correction also to the curvature bispectrum. To quantify the impact of the correction, the equilateral mode-scale configuration has been adopted. This assumption leads directly to the analytical computation of the amplitude of the overall correction which is clearly very interesting from an observational point of view since it can constraint the parameters of the model. However a full characterization of the bispectrum shape due to quantum decoherence was still missing. Indeed, what we will do in the present thesis is to solve numerically a system of equations governing the bispectra evolution in the most general way. In this manner we will obtain the overall shape of the induced bispectrum which will depend on the parameters of the model. The shape is particularly interesting since it suggests for which configurations the effect of decoherence is peaked.