Vacuum decay, warm inflation and its connections with the current accelerated stage of the universe: conceptual aspects and observational tests

Abstract

The current standard cosmological model still has several conceptual problems. One of them is the fine tuning needed in both inflation models and in models describing the present state of accelerated expansion of the universe. In the new inflationary scenario, for example, is difficult to reconcile a period of rapid expansion with the subsequent reheating of the universe, as it requires fine-tuning on the parameters of the theory. One possibility to solve this problem is the warm inflation scenarios, in which energy dissipation mechanisms are considered during the inflationary phase. This scenario has proven extremely robust and capable of solving problems that other variants are proposed to solve. In this project we propose to investigate how processes out of thermodynamic equilibrium affect the rate of expansion of the universe at different stages of the universe and, in particular, how these processes influence the inflationary period, emphasizing the warm inflation scenario. We will also consider a possible connection between the inflationary period of the early universe and the current accelerated expansion of the universe. We will calculate the density fluctuations generated in this scenario and the results will be compared with data from cosmic microwave background and large scale structure, so that we can distinguish between different models of warm inflation. We will also discuss the stochastic behavior of the warm inflation from the point of view of more realistic viscosities, using for example, mechanisms that introduces time-dependent viscosities and colored noises in the Langevin equation. Finally we will investigate a possible physical equivalence between the phenomenological models with decaying vacuum and gravitational particle creation and its connections with scenarios of warm inflation. (AU)