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