Phase transitions in the early universe

Thesis

Phase transitions are a generic prediction of models in particle physics. In the Standard Model, for example, there are two phase transitions: the QCD confinement transition and the electroweak phase transition, both occurring in the very early stages of the universe. Many extensions to the Standard Model predict new phase transitions, all occurring at very high temperatures. Depending on how these transitions proceed they may lead to signatures which can be detected today, offering a way to probe the early stages of the universe.

This thesis is on phase transitions and their impacts on early universe cosmology. Chapter 1 is an overview of the physics of phase transitions, both in the Standard Model and extensions of it. The different phases of gauge theories are described before discussing the phase transitions in the Standard Model and general features of phase transitions in theories beyond the Standard Model. The cosmological implications of these transitions is then summarised, with a focus on the production of topological defects, the gravitational wave signal and constraints from supercooling.

Chapter 2 focuses on the confining transition in Randall-Sundrum models. The transition places severe cosmological constraints on the model, meaning the model is only marginally under parametric control as an effective field theory. In this chapter a mechanism is presented which circumvents the problematic phase transition by making the confined phase metastable at high temperatures. The phenomenological features of the model, in particular dark matter production, are also presented in this chapter.

Everyday phase transitions are often catalysed by the presence of defects or impurities in the material, leading to an enhanced transition rate. In cosmology, however, phase transitions are typically considered to proceed from a homogeneous initial state. In chapter 3 the possibility that magnetic monopoles could act as catalysts for cosmological phase transitions is considered, and an algorithm developed to solve the field equations describing the transition. A similar idea is pursued in chapter 4 for the case of domain walls catalysing the electroweak phase transition.

Authors: Nee, M

• DOI: 10.5287/ora-8nrvyz6gz
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: extra dimensions; topological defects; particle physics; phase transitions; dark matter; gravitational waves; cosmology
• Subjects: Gravitational waves; Broken symmetry (Physics); Cosmology; Magnetic monopoles