Effects of heavy fields on inflationary cosmology

Cosmological inflation is the most successful theory that explains the homogeneity and flatness of the early universe. It also provides a quantum origin for the primordial perturbations that we observe in the Cosmic Microwave Background Radiation (CMB). The simplest models make use of a single scalar field, which produces the exponential expansion of the early universe. In this thesis the effects of additional heavy fields is studied from several points of view. On the one hand, possible signatures due to the presence of such fields are searched for in the current CMB data, and a new formalism is developed, allowing the analytical study of features arising from the presence of these fields. On the other hand, in the context of supergravity theories, the presence of additional heavy fields is ubiquitous, and their stability is needed in order to not spoil the basic predictions of single-field inflation. The viability of inflation in the presence of an additional heavy supersymmetric sector is studied, and several stability constraints are derived. The conclusion is that CMB data might be already sensitive enough to the presence of additional heavy fields, and that the landscape of supergravity scenarios which stabilize these fields is very constrainedTheoretical Physic