Non-Gaussianities from a kinetic pre-inflationary universe

Thesis report for the title of MASt in Physics from the University of Cambridge, 2022.

Abstract:

Modern inflation theory is based on Mukhanov-Sasaki equations which give a perturbative framework to propagate initial quantum fluctuations as sources of the Cosmic Microwave Background (CMB) anisotropies encountered at the recombination epoch. Following previous work on initial conditions for the power spectrum, this work extends the kinetic pre-inflation model to the derivation of the primordial bispectrum, related to 3-point correlations. We derive here the slow-roll era contributions to the bispectrum thanks to the In-In formalism for different initial conditions. In addition to an oscillating locally-shaped bispectrum, it is found that the dependence on the time and nature of the transition between pre-inflation and inflation is strong. As a main result, new UV and IR divergences are encountered for the non-Gaussianities, showed to be independent of the choice of the vacuum. Finally, the validity of the calculus is tackled in an EFT framework and paves the way for conclusions on further needed work.

[Uploaded 17/11/23]