INFLATIONARY PREDICTIONS IN EXTENSIONS TO THE STAROBINSKY MODEL

Cosmology is the science trying to understand the nature of the Universe and its evolution. Inflation, the theory proposing a period of accelerated expansion in the very early stages of the Universe, aims to answer a number of questions arising in the standard Big Bang cosmology, like the flatness problem, the horizon problem and the origin of large-scale structures.
Inflation is usually assumed to be driven by scalar fields. The aim of this thesis is to investigate predictions of the Starobinsky model and its extensions, where an inflationary phase is driven by corrections to General Relativity. First proposed in 1980 by A. Starobinsky, he showed that corrections to General Relativity could drive an accelerated expansion in the early Universe. Here we extend this theory by adding a matter field which influences the inflationary dynamics and discuss how the predictions are altered. We find that the extended model is in excellent agreement with the latest observational results by the Planck collaboration. We also study the running of the spectral index and higher orders parametrisations of the power spectrum and compare them to predictions in other inflationary models.
Finally we are investigating the theory of reheating in the extended Starobinsky model. We show that the corrections to General Relativity have an effect on the duration of reheating during perturbative reheating and that they reduce the efficiency of particle production in parametric resonance reheating. Thus it becomes clear that these effects need to be taken into account when comparing theoretical results to data.