New approaches to quantum cosmology
File(s)
Author(s)
Alexandre, Bruno
Type
Thesis
Abstract
This thesis explores various foundational aspects of quantum cosmology and gravity theories through the lens of unimodular gravity and gauge-theoretic frameworks. We begin by investigating the feasibility of employing multiple simultaneous relational clocks. Subsequently, we study quantum cosmological models describing the transition from a decelerated to an accelerated expansion of the universe. The implications for the Hubble parameter are examined from both matter and cosmological constant perspectives.
Revisiting the Hartle-Hawking wave function, we demonstrate that unimodular gravity in the connection representation yields a unitary quantum theory with normalizable wave packets. Attempting a similar analysis for the Vilenkin wave function reveals inherent difficulties, prompting proposals for structural adjustments to ensure unitarity and semiclassical normalizability.
We further investigate classical signature changes in degenerate metrics, elucidating their cosmological implications and relationships with the cosmological constant.
Extending the Plebanski formulation, we introduce a Higgs mechanism for the Ashtekar connection, exploring its cosmological outcomes and gravitational wave predictions.
In two-dimensional contexts, Jackiw-Teitelboim gravity is analyzed via a gauge-theoretic unimodular approach.
Finally, we propose a graviweak unification model, suggesting parity-breaking spontaneous symmetry mechanisms as the origin of gravity-weak interactions, further generalized through MacDowell-Mansouri frameworks.
Revisiting the Hartle-Hawking wave function, we demonstrate that unimodular gravity in the connection representation yields a unitary quantum theory with normalizable wave packets. Attempting a similar analysis for the Vilenkin wave function reveals inherent difficulties, prompting proposals for structural adjustments to ensure unitarity and semiclassical normalizability.
We further investigate classical signature changes in degenerate metrics, elucidating their cosmological implications and relationships with the cosmological constant.
Extending the Plebanski formulation, we introduce a Higgs mechanism for the Ashtekar connection, exploring its cosmological outcomes and gravitational wave predictions.
In two-dimensional contexts, Jackiw-Teitelboim gravity is analyzed via a gauge-theoretic unimodular approach.
Finally, we propose a graviweak unification model, suggesting parity-breaking spontaneous symmetry mechanisms as the origin of gravity-weak interactions, further generalized through MacDowell-Mansouri frameworks.
Version
Open Access
Date Issued
2025-07-01
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Magueijo, Joao
Sponsor
Fundacao para a Ciencia e a Tecnologia
Grant Number
FCT Grant No. 2021.05694.BD
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)