Physics & Astronomy ETDs

Publication Date

Spring 5-17-2025

Abstract

The dominant Lambda Cold Dark Matter (LCDM) cosmological model, while remarkably successful, increasingly shows signs that it may not fully describe our Universe, as persistent tensions in expansion rates and structure formation remain unresolved. In this thesis, I challenge the LCDM paradigm using novel theoretical frameworks combined with rigorous numerical analyses. I demonstrate that the expansion-rate tension fundamentally reflects underlying distance disagreements, and that the Thomson scattering rate strongly restricts higher pre-recombination expansion rates without additional physics. Further, I present a novel cosmological model using a mirror dark sector and varying fundamental constants, revealing an observational degeneracy allowing significantly higher expansion rates while remaining consistent with data. Lastly, I show that detectable B-mode polarization signals can originate from phase-transition-induced gravitational waves, challenging the long-held view of primordial B-modes as definitive evidence for inflation. Collectively, this work advances our understanding of cosmic tensions and suggests clear avenues for future research.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Francis-Yan Cyr-Racine

Second Committee Member

Rouzbeh Allahverdi

Third Committee Member

Darcy Barron

Fourth Committee Member

Gordan Krnjaic

Fifth Committee Member

Dinesh Loomba

Language

English

Keywords

Hubble tension, Recombination, Cosmic Microwave Background, Phase Transitions, FFAT Scaling

Document Type

Dissertation

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