Formation and interactions of topological defects and their role in cosmology

Details Formation and interactions of topological defects and their role in cosmology Formation and interactions of topological defects and their role in cosmology

Jul 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt........10p&link_type=abstract

Thesis (PhD). CASE WESTERN RESERVE UNIVERSITY, Source DAI-B 62/01, p. 291, Jul 2001, 132 pages.

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We have studied the formation, interactions and cosmological implications of topological defects. The following original contributions are presented in this thesis. We introduce a scheme for numerically investigating the formation of cosmic strings without assuming the geodesic rule. Our results show that the fraction of string in infinite strings grows as we deviate from the geodesic rule. We study the interaction of magnetic monopoles and domain walls in a model with SU (5) × Z2 symmetry by numerically evolving the field equations. The simplest domain wall has the structure of a kink across which the Higgs field changes sign. We find that the monopoles unwind and dissipate their magnetic energy on collision with kinks. We further show that the kink solution in SU(5) is perturbatively unstable for all parameters. We then construct a domain wall solution that is lighter than the kink and show it to be perturbatively stable for a range of parameters in renormalizable potentials. The symmetry in the core of this domain wall is smaller than that outside. The interactions of the domain wall with magnetic monopole is discussed and it is shown that magnetic monopoles with certain internal space orientations relative to the wall pass through the domain wall. We investigate the effect of wiggly cosmic strings on the cosmic microwave background radiation anisotropy and matter power spectrum. For the same choice of simulation parameters we have compared the results with and without including wiggliness in the model and found that wiggliness together with the accompanying low string velocities lead to a significant peak in the microwave background anisotropy and to an enhancement in the matter power spectrum. We also show that within the considered string model, the position of the main peak in the CMB power spectrum corresponds to a closed universe with Ω = 1.3. Despite improvements introduced by including the wiggliness and by going to a closed universe, all models of structure formation based solely on cosmic strings are ruled out by data from BOOMERANG and MAXIMA experiments. We present a new method for the computation of the third moment of the photon brightness temperature perturbation from active models of structure formation. We apply it to estimate the bispectrum of the cosmic microwave background temperature anisotropies generated by wiggly cosmic strings.

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