The very early universe: an analysis on inflationary and collapsing scenarios.

Abstract

Inflation is an accelerated expansion that may occurred at very high energy in the early Universe. In addition to bringing a solution for the hot big bang model problems, it also provides an effective mechanism for the production of cosmological fluctuations, which give rise to the large scale structures as we see today. However, it is important to highlight that inflation is not the only mechanism capable of solving the initial issues of our Universe. Collapsing scenarios can be an alternative option to originate the hot Big Bang and the primordial perturbations. In the first part of this thesis, we present the inflationary scenario, with emphasis on the Starobinsky model, discussing its general set-ups, predictions and a possible modification to the R2 inflation motivated by the-Attractors. The second part is dedicated to the analysis of collapsing scenarios, based on a scalar field with exponential potential with inclusion of the stochastic formalism, which allows us to compute the stochastic noise generated by the quantum fluctuations crossing into a coarse grained, super-Hubble scalar field