The deviation from a Gaussian statistics in the CMB temperature anisotropies is an observable capable to discriminate among different scenarios of generation of the primordial perturbations during the inflationary epoch. In the present work we study the contributions to the non-linear temperature anisotropies on large scales, in order to give a prediction for the bispectrum which is the main statistical tool sensitive to the level of non Gaussianity. After a review of the inflationary paradigm and of cosmological perturbation theory up to second order, we discuss some of the proposed scenarios of generation of the primordial perturbations; then, we will follow the evolution of non linearities by exploiting the conservation on large scales of the gauge-invariant curvature perturbation, and finally we study the transfer of these non linear perturbations to the temperature anisotropies on large scales. In this way, we are able to provide an expression for the true non linearity parameters measured by the present generation of CMB satellite experiments, taking into account the initial conditions set during (or immediately after) inflation and the subsequent gravitational evolution. A non-perturbative approach is used to obtain the evolution equations and the expression for the temperature fluctuations on large scales, with the idea it can help to study signals of non-Gaussianity different from the bispectrum.
NON-GAUSSIANITY OF LARGE-SCALE CMB ANISOTROPIES: A NON-PERTURBATIVE APPROACH
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