2026-05-21T00:29:44Zhttps://keep.lib.asu.edu/oai/requestoai:keep.lib.asu.edu:node-1581522024-12-20T18:25:12Zoai_pmh:alloai_pmh:repo_items158152
https://hdl.handle.net/2286/R.I.57100
http://rightsstatements.org/vocab/InC/1.0/
2020
133 pages
Doctoral Dissertation
Academic theses
Text
eng
Saurabh, Ayush
Vachaspati, Tanmay
Lebed, Richard
Baumgart, Matthew
Keeler, Cynthia
Arizona State University
Doctoral Dissertation Physics 2020
In this dissertation, I present the results from my recent <br/><br/>investigations into the interactions involving topological defects, such as <br/><br/>magnetic monopoles and strings, that may have been produced in the early <br/><br/>universe. I performed numerical studies on the interactions of twisted <br/><br/>monopole-antimonopole pairs in the 't Hooft-Polyakov model for a range of <br/><br/>values of the scalar to vector mass ratio. Sphaleron solution predicted by <br/><br/>Taubes was recovered, and I mapped out its energy and size as functions of <br/><br/>parameters. I also looked into the production, and decay modes of $U(1)$ gauge <br/><br/>and global strings. I demonstrated that strings can be produced upon evolution <br/><br/>of gauge wavepackets defined within a certain region of parameter space. The <br/><br/>numerical exploration of the decay modes of cosmic string loops led to the <br/><br/>conclusions that string loops emit particle radiation primarily due to kink <br/><br/>collisions, and that their decay time due to these losses is proportional to <br/><br/>$L^p$, where $L$ is the loop length and $p \approx 2$. In contrast, the decay <br/><br/>time due to gravitational radiation scales in proportion to $L$, and I <br/><br/>concluded that particle emission is the primary energy loss mechanism for loops <br/><br/>smaller than a critical length scale, while gravitational losses dominate for <br/><br/>larger loops. In addition, I analyzed the decay of cosmic global string loops <br/><br/>due to radiation of Goldstone bosons and massive scalar ($\chi$) particles. <br/><br/>The length of loops I studied ranges from 200-1000 times the width of the <br/><br/>string core. I found that the lifetime of a loop is approximately $1.4L$. The <br/><br/>energy spectrum of Goldstone boson radiation has a $k^{-1}$ fall off, where $k$ <br/><br/>is the wavenumber, and a sharp peak at $k\approx m_\chi/2$, where $m_\chi$ is <br/><br/>the mass of $\chi$. The latter is a new feature and implies a peak at high <br/><br/>energies (MeV-GeV) in the cosmological distribution of QCD axions.
Particle Physics
cosmic strings
global strings
Magnetic monopoles
Solitons
Toplogical Defects
vortices
Phenomenology of Topological Solitons