Modeling and constraining inflationary and pre-inflationary eras
The paradigm of cosmic inflation has had great success in explaining the statistical properties of fluctuations in the Cosmic Microwave Background (CMB). In this dissertation we discuss a few avenues for modeling and constraining the inflationary universe - constraints on excited states of inflationary fluctuations, some aspects of multi-field tunneling and also constraints on and predictions from a specific model of inflation connecting Higgs physics and dark matter. First, we show that in standard single field slow roll inflation, Bogoliubov excitations of the fluctuation spectrum are tightly constrained by observations. These constraints ensure that the squeezed limit non-gaussianity obtained from such excited states cannot be large. They also rule out any significant imprints in the CMB coming from a sudden transition from kinetic energy domination to inflation. We then explore tunneling in the context of field theory, a scenario that has potential relevance to the pre-inflationary universe. We discuss subtleties involved in choosing the trajectory for tunneling out of a metastable vacuum in a multi-field potential. In particular, we use exact solutions and scaling relations to show that tunneling may happen along directions with large barriers, thus making the common intuition coming from quantum mechanical tunneling unreliable in estimating the tunneling trajectory and therefore, the bounce action. We then explore a specific model of inflation that involves the addition of a scalar singlet and fermionic dark matter to the standard Higgs inflation scenario. We show that dark matter constraints and the requirement to support successful inflation significantly constrain the available parameter space for this model. We also find that the model generically predicts a small value of the tensor-to-scalar ratio r, similar to standard Higgs inflation, though it allows for a larger range of values for the scalar spectral tilt nS.