Ultraviolet complete inflation: looking at inflation from fundamental physics

To completely describe the inflationary era in the early universe is an extremely ambitious task. The main reason is that its dynamics are highly sensitive to ultraviolet physics, making the knowledge of inflation dependent on our ignorance of what is happening at these energy scales. This is not necessarily a weakness of inflation as a paradigm; it is ultimately its most interesting characteristic. Accepting this lack of control on the details of inflationary dynamics brings observational cosmology and the search for an ultraviolet complete theory of gravity together. In this thesis, this duality is explored with the aim of making steps towards an efficient way of studying inflation and its predictions and signatures. This challenge is twofold; first, since fundamental theories are far from being able to explicitly determine the early universe physics, the construction of approximate toy models is unavoidable. For this reason, I identify the key issues for the building of a realistic inflation model, in particular the delicate flatness of the inflaton potential, the strong possibility of multifield dynamics and the necessity of a viable reheating, and in the light of these analyze how best to approximate an ultraviolet complete inflation. For this analysis, two different classes of case studies are presented: inflation in the brane picture and in a holography inspired scenario. On the other hand, since any toy model of an ultraviolet complete inflation necessarily presents a high level of complexity, the computation of predictions for observables is not trivial. For this purpose, I develop numerical tools that manage to compute these parameters efficiently and with a high level of accuracy for a broad range of inflation classes with more than one active field. For each case study, I determine the impact of the inclusion of microphysics contributions in the resulting observational signatures and confront them with data.