Departmental Oral Examination (Thesis Title: "Investigating the Dark Sector of the Universe Using Cosmological Observables")
Physics and Astronomy
Although the Standard Model of particle physics has been a phenomenal success in modelling known particles and predicting new, theoretically founded particles, it is known to be incomplete. Although the Standard Model of cosmology has been a phenomenal success in modelling the evolution of the Universe, it too has open questions that remain unresolved. In this thesis, we aim to address properties of new physics models that are being developed that aim to answer these open questions. In particular, we wish to focus on and examine in detail the connection between the dark sector of the Universe and the visible sector. In examining this connection, we may use cosmological observables to place strict limits on new theories that go beyond the Standard Model.
In the first part of this thesis we will address the flow of energy from the visible sector to the hidden via a phenomenon known as freeze-in. Here, we explore the effects that early-time, ultraviolet energy transfer may have on the infrared, late-time evolution of a dark matter candidate. We use a simplified hidden-sector model to highlight the notion that operators that are typically considered early may have relevant late-time effects.
Following this, we consider the reverse energy flow, and consider how dark-sector energy injection via decays of electromagnetic radiation may affect the products of Big Bang Nucleosynthesis. In this section, we focus on arbitrary light particle (< 100 MeV) decays, and identify how direct and indirect alteration of the light element abundances can be constrained using the measured values today. Direct alteration is caused by photodissociation, while indirect effects are felt through changes in the radiation energy density.
Finally, we consider a full and rich dark sector, consisting of a non-Abelian SU(3) gauge force. This new gauge field presents itself as glueballs after a confining transition. We study the effects of this confining transition, as well as the subsequent dynamic evolution of the spectrum of glueballs produced. In the final chapter, we examine how decays to Standard Model particles via higher-dimensional, non-renormalizable operators can place stringent limits on the parameter space of this gauge force.