Aspects of the Electroweak Theory

Porter, Helen Julia (1990) Aspects of the Electroweak Theory. PhD thesis, University of Glasgow.

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Abstract

This thesis is divided into two quite distinct parts, linked only by the central role of the electroweak theory in each. The first part is concerned with the experimentally observed DeltaI =1/2 selection rule in weak Kaon decays, and we consider an extension to the Standard Model which might allow a satisfactory theoretical explanation of the rule. The second part forms the major part of the thesis and is related to the well-known baryon asymmetry of the Universe. We explore the possibility that the non-perturbative sector of the electroweak theory could play a central role in the production of such an asymmetry. We use lattice gauge techniques to simulate the electroweak interactions in the phase with restored SU(2) symmetry and numerically calculate a rate for baryon number non-conservation processes which is then compared to the existing theoretical predictions. Ma has recently proposed an extension to the Standard Model which contains new penguin diagrams and which should therefore contribute to DeltaI = 1/2 processes. The new model must be constrained to preserve the observed small KL-KS mass difference. We correct and reanalyse the model and search the parameter space numerically to find suitable values for the new particle masses. We find that that the model is unable to provide the necessary enhancement to fully understand the rule. The electroweak theory may play a major role in the generation of the baryon asymmetry of the Universe. It provides for fermion number non-conservation by allowing sphaleron type transitions across the potential barrier separating different topological sectors. These transitions are thought to become rapid at high temperature, but perturbative calculations are not possible because of infrared singularities. We have used lattice gauge theory to study the evolution of an SU(2) gauge-Higgs system in the high temperature, unbroken symmetry phase. A Minkowski metric was used so that we were able to measure the rate of sphaleron transitions in real time, by following the development of the Chern- Simons number, Ncs, which is closely related to the topological charge. We include a description of the problems relating to the measurement of topological quantities on the lattice and compare the results of using different techniques to measure them. Using 8.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: High energy physics, Theoretical physics
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78194
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:37
Last Modified: 30 Jan 2020 15:37
URI: http://theses.gla.ac.uk/id/eprint/78194

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