Author ORCID Identifier

https://orcid.org/0000-0003-4230-8137

Date of Award

Spring 6-10-2023

Document Type

Thesis (Ph.D.)

Department or Program

Physics and Astronomy

First Advisor

Robert Caldwell

Abstract

In this thesis I explore two main topics: the role and consequences of cosmological vector fields, and new ideas for constraining fundamental physics with state-of-the-art experiments. These topics are disparate in content and technique but unified in their attempt to leverage novel approaches to better understand longstanding questions in cosmology. These questions, such as ``What is causing the universe to accelerate today?'' and ``What are the neutrino masses?'', underpin the modern cosmological paradigm. They play a key role in our understanding of cosmic history, the formation of structure, and the fate of our universe. Answers to or hints about these questions would have wide-reaching consequences for cosmology, astronomy, particle physics, and gravitational physics.

In Chapter 1 I explore the consequences of relic cosmological vector fields which may be left over from the early universe. I demonstrate that these relics can significantly transform the shape, amplitude, and net circular polarization of a stochastic gravitational wave background (SGWB) and I point out the consequences for detecting such a background both directly and via cosmic microwave background (CMB) polarization. Additionally, I show the impact of scalar and vector perturbations on cosmic observables is negligible.

In Chapter 2 I introduce a novel model of late-time cosmic acceleration which relies on a coupling between a scalar and gauge fields. This model achieves slow roll dynamically and can drive dark energy without fine tunings. Importantly, this model generically predicts a suppression of an SGWB, with implications for both the experimental search for GWs and for distinguishing this model from standard scenarios. The last sections of this chapter are dedicated to further developing the theory necessary to compute the CMB anisotropies.

I change gears in Chapter 3, shifting focus to broadly constraining theory with clever analysis of cosmological data. I demonstrate the power of combining measurements of the CMB and large-scale structure to measure the sum of the neutrino masses and deviations from general relativity. I show how utilizing the reconstruction of velocities from tomographic measurements improves our ability to constrain these important physical quantities, and I discuss prospects for further advancement.

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