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Title: Microphysics of cosmic strings in supersymmetric and grand unified theories
Author: Davis, S. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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In this thesis we investigate the microphysics of cosmic strings in non-minimal quantum field theories. In particular we consider theories in which fermion fields couple to the strings, and those with larger symmetry groups, such as grand unified and supersymmetric theories. By considering these extensions to the minimal model, we obtain a more realistic picture of the properties of cosmic strings. In considering grand unified theories, which have multiple phase transitions, we show that a cosmic string formed at one phase transition can cause the creation of another string-line solution at a later transition. This string-like solution will have many of the properties and implications of a normal cosmic string. We consider this effect for a general string solution, and illustrate it with a realistic SO(10) unified theory. As well as the usual abelian strings, this theory also contains more exotic string solutions. We consider both types of cosmic string. Separately, we examine the form of cosmic string solutions in supersymmetric theories, and the effect of soft supersymmetry breaking on them. We investigate the existence of conserved fermion currents in a variety of cosmic string models. We show that supersymmetry may be used to find the form of some solutions analytically. We also derive an expression for the number and type of massless fermion currents in a general model. The existence of conserved current can conflict with observations, so these results may be used to constrain models. We find the number of massless currents in the SO(10) and supersymmetric theories mentioned above. We show that currents present on a string can be destabilised by later phase transitions or supersymmetry breaking. This may allow any conflict that the current's existence has with observations to be avoided. We also examine massive fermion currents in a simple model, and determine the spectrum of such states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available