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

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.