Observable signatures of multi-field inflation

Inflation is the standard paradigm able to give rise in a dynamical way to the current state of the universe without imposing extremely fine-tuned initial conditions and, when combined with quantum mechanics, it also provides an explanation for the temperature anisotropies in the CMB. Such latter property can be used in order to test the inflationary models and to select the best to describe the data. This thesis focuses on multi-field inflationary realizations, in particular on the case with two-fields, which are both observationally viable and theoretically well motivated by the attempt to embed inflation within a UV completion framework like string theory. Multi-field inflationary models are characterized by specific observable signatures like enhancements in the power spectrum. The latter result follows from the presence of non-negligible iso-curvature perturbations acting as source terms for the curvature ones. The parameter associated to the turning of the inflationary path is η⊥. The orthogonal component of the second slow-roll parameter acts as the coupling between curvature and iso-curvature modes. Trajectories with a higher value of η⊥ are those for which purely multi-field effects are more intense. In this thesis we study a particular model of multi-field string inflation, known as Roulette inflation, in which both the real and the imaginary components of the kahler modulus T (i.e. the 4−cycle volume τ and the axionic partner θ) are dynamical and determine inflation and from such a two-field setting a wide variety of possible trajectories to analyze emerges. Among them, some realizations lead to specific and new signatures, resulting into a first step towards a more in depth analysis of related models.