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Title: Pseudo-Goldstone bosons in early universe physics
Author: Croon, Djuna Lize
ISNI:       0000 0004 6422 9090
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2017
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This thesis aims to give an approach to dealing with Hierarchy problems in theoretical physics, plaguing theories that span a wide range of energy scales. At present, any theory that is formulated to connect observations of the Early Universe to results in present day particle physics, exhibits the necessity of (at least one) unnaturally fine-tuned parameter. This has encouraged the sectioning of of many separate, highly specialized fields - each dealing with Effective Field Theories (EFTs) valid at a limited range of energy scales only. Here I describe an effort to connect different energy scales while dynamically accounting for hierarchies. This thesis discusses the appeal of pseudo-Goldstone bosons (pGBs) for the generation of scales in Early Universe cosmology. In particular, I will show how models with pGBs address the radiative instability of mass scales in quantum mechanical theories. I will start with an introduction to the two hierarchy problems that will be the primary focus of the thesis: the electroweak hierarchy problem, or the puzzle of the lightness of the Higgs mass; and the inflationary hierarchy problem, or the flatness of the inflaton potential demanded by the nearly scale invariant spectrum of the Cosmic Microwave Background. I will briefly introduce how pGBs arise, and can be described, using an example of a compact Special Orthogonal group SO(n) breaking to its largest coset SO(n - 1). I will then explore various models that address the electroweak and the inflationary hierarchy problem, using appropriate EFT tools such as the Callan-Coleman-Wess-Zumino mechanism and 5D approaches. I will discuss the relative strength of these models compared to existing models in the literature. After this discussion I will show that it is possible to address both hierarchy problems in a unified model, in which an inflaton decays into the Higgs field after inflation, in a process called reheating. This section will include a detailed derivation of the model, and will explore the regions of parameter space that lead to inflation, reheating, and electroweak symmetry breaking compatible with the relevant experimental data. This is followed by an excursion in which I will discuss non-compact models, based on SO(n;1)=SO(n) cosets. I will show how such setups can also give rise to inflation compatible with the current data, and discuss different scenarios for reheating. I will finish with an epilogue of the prospects of (holographic) Composite Higgs models - in which the Higgs is a pGB of the breaking of a strong compact symmetry - at particle colliders.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC0801 Geophysics. Cosmic physics