Thermal Inflation with a Thermal Waterfall Scalar Field Coupled to a Light Spectator Scalar Field

TL;DR

This thesis introduces a new Thermal Inflation model where the waterfall field's mass depends on a light scalar, analyzing its potential to generate primordial curvature perturbations and its observational signatures.

Contribution

The paper develops a novel Thermal Inflation model with a coupled scalar field, exploring its parameter space and observational predictions using the $ abla N$ formalism.

Findings

Certain parameter regions exclude the model as the dominant source of curvature perturbations

The model predicts specific non-Gaussianity and spectral index signatures

Some parameter choices yield sharp, testable predictions for inflationary observables

Abstract

This thesis begins with an introduction to the state of the art of modern Cosmology. The field of Particle Cosmology is then introduced and explored, in particular with regard to the study of cosmological inflation. We then introduce a new model of Thermal Inflation, in which the mass of the thermal waterfall field responsible for the inflation is dependent on a light spectator scalar field. The model contains a variety of free parameters, two of which control the power of the coupling term and the non-renormalizable term. We use the $\delta N$ formalism to investigate the "end of inflation" and modulated decay scenarios in turn to see whether they are able to produce the dominant contribution to the primordial curvature perturbation $\zeta$. We constrain the model and then explore the parameter space. We explore key observational signatures, such as non-Gaussianity, the scalar spectral index and the running of the scalar spectral index. We find that for some regions of the parameter space, the ability of the model to produce the dominant contribution to $\zeta$ is excluded. However, for other regions of the parameter space, we find that the model yields a sharp prediction for a variety of parameters within the model.