A comparison between standard slow-roll inflation and warm inflation

Inflation is a postulated period of accelerated expansion that took place well within the first seconds of the universe and that provides initial conditions for the following cosmological evolution that are in excellent agreement with observations. At the end of inflation, the inflaton field (the source of the inflationary expansion) is supposed to decay into other fields. This process, known as reheating, generates the thermal bath of the hot big-bang era. In some models, the couplings of the inflaton can be relevant already during inflation, leading to an effective dissipative dynamics. In this thesis we critically review the two distinct scenarios in which these dissipative effects are either negligible or relevant during inflation. The first type of models belong to the more standard class of theories of slow-roll inflation. For the second case, we focus our attention on the so called models of warm inflation, in which the dissipation sustains a bath of particle in thermal equilibrium: the interaction between the inflaton and this bath entails an overdamped motion for the homogeneous inflaton field, allowing inflation in potentials that would otherwise be too steep to support the slow-roll conditions, and it also significantly modifies the primordial perturbations. We study the background evolution, the primordial perturbations and the phenomenology of these two scenarios.