Cosmological Perturbations from Hybrid Potentials

TL;DR

This paper investigates hybrid inflation models, analyzing their parameter space against observational data from PLANCK, and finds certain configurations compatible with current cosmological measurements, including models with additional scalar fields.

Contribution

The study constrains hybrid inflation models using observational bounds and explores a supersymmetric version with a third light scalar field compatible with data.

Findings

Large parts of parameter space are ruled out by spectral index and non-gaussianity constraints.

Certain hybrid inflation models remain viable within observational bounds.

Supersymmetric hybrid inflation with a third scalar field can produce observable predictions consistent with data.

Abstract

Cosmological inflation is the dominating paradigm to account for observations of the Cosmic Microwave Background (CMB). In this thesis, we study the phenomenology of a class of particularly well motivated models of inflation, known under the generic name of hybrid models. They are characterised by a transition from a valley to a hilltop shaped potential. In particular, we study three limiting regimes of the simplest realisation, hybrid inflation, constraining its parameter space using observational bounds on the spectral index and the non-gaussianity of the primordial perturbations. We find that the model is highly constrained by observations, with large part of the parameter space either ruled out by a blue spectral index ($n_s>1$) or by a large non-gaussianity parameter $f_{rm NL}$, two quantities measured with precision by PLANCK. However, there exists regions in parameter space leading to interesting phenomenology compatibly with observational bounds. Also, a version of hybrid inflation with a third light scalar field at horizon crossing is derived from the supersymmetry framework. We find that the model can generate observables within observational bounds.