Abstract
dc:description.abstractThis thesis presents two papers [1,2] published by the author with collaborators as cited. It fits within the Kähler sector of Type IIB SUGRA constructions, and more generally the field of string theory phenomenology. The intrinsic appeal of super string theory as a candidate theory for quantum gravity is its completeness, only one parameter (the string length/scale) is input to the theory and then the rest of the story is generated dynamically and by enforcing the normal physicality constraints. However, we start with a supersymmetric theory in 10 dimensions, and the goal of the field is to connect this UV theory with the 4 dimensional, non supersymmetric, IR world we observe. Principally, the question of how to compactify the 10d theory on appropriate internal manifolds such that all scalar fields are fixed with appropriate masses to resemble our IR observations is the most important question within the field. In this thesis we, in the first couple of chapters, introduce and review the established literature to establish our Type IIB SUGRA theories as low energy limits of string theory and then highlight progress made in answering this question. In Chapter 3 we review the work of [1] and present our progress in a comprehensive study of Kähler moduli stabilisation within Type IIB flux compactifications, combining advanced numerical techniques with analytical methods. Our JAX-based computational framework enables efficient scanning of the UV parameter space, while incorporating α′ corrections, loop and non-perturbative effects, as well as uplift contributions to the scalar potential. The implementation features rigorous vacuum validation protocols derived from analytic results. We apply our methods to explicit flux compactifications on more than 80,000 Calabi-Yau threefolds with h1,1 ≤ 6 Kähler moduli. By systematically scanning over a wide range of values of the flux superpotential W_0 and the string coupling g_s, we find explicit realisations of every established Kähler moduli stabilisation scenario: for 10^{-15} ≤ |W_0| ≤ 10^{-2} we obtain both KKLT-like and Kähler uplifted vacua, while for the broader range 10^{-1} ≤ |W_0| ≤ 10^2 we recover LVS and LVS-like hybrid solutions. Notably, we discover significant parameter regions where multiple vacua coexist within a single flux potential, including novel configurations pairing AdS, Minkowski, and dS minima with different volume hierarchies. These findings enable, for the first time, the analysis of vacuum decay processes within fixed flux configurations, complementing the established theory of transitions between distinct flux vacua and decays towards decompactification. In Chapter 4 we review the work of [2]. Here, we study a new framework for brane-antibrane inflation where moduli stabilisation relies purely on perturbative corrections to the effective action. This guarantees that the model does not suffer from the eta-problem. The inflationary potential has two contributions: the tension of an antibrane at the tip of a warped throat, and its Coulomb interaction with a mobile brane. This represents the first realisation of the original idea of brane-antibrane inflation, as opposed to inflection point inflation which arises when the moduli are fixed with non-perturbative effects. Moreover, we formulate the brane-antibrane dynamics as an F-term potential of a nilpotent superfield in a manifestly supersymmetric effective theory. We impose compatibility with data and consistency conditions to ensure control over the approximations and find that slow-roll inflation can occur in a large region of the underlying parameter space. The scalar spectral index is in agreement with data and the tensor-to-scalar ratio is beyond current observational reach. Interestingly, after the end of inflation the volume mode can, but does not need to, evolve towards a late-time minimum at larger values. In Chapter 5 the thesis is then summarised and concluded. Various supplementary and extended discussions / calculations are detailed in the accompanying appendices.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2025
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Hughes, Christopher
- Advisor dc:contributor.advisor
-
- Quevedo, Fernando
Subjects
dc:subject × 7Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.125267
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/395919