| Summary: | In this thesis we will examine topological defects that arise in various physical
contexts. The main theme of this thesis is the study of matter at high
densities and low temperatures. This is important as these are the conditions
that are realized in the interior of a neutron star. The first part of
this thesis is devoted to the study of topological defects that appear in the
color superconducting phase of high density QCD. We will show that unlike
the Standard Model at zero density, the Standard Model at large densities
supports various types of topological defects. In particular, we will assess
the stability of the domain walls at intermediate densities. We will also
show that there exists vortices that have a nonzero condensate trapped on
the core. The consequence of the nonzero condensate is that it is possible
to form stable loops of these strings called vortons. Next, we will examine
matter at slightly smaller densities below the point where the color superconducting
phase of QCD occurs, where the ground state consists of Cooper
pairs of neutrons and Cooper pairs of protons. The presence of an electrically
charged proton condensate leads to conventional BCS superconductivity. In
this thesis we will demonstrate that the presence of a neutron condensate
leads to type-I superconductivity, contrary to the standard picture that the
interior of a neutron star exhibits type-II superconductivity. The final part of this thesis will introduce vortons in the context high temperature superconductivity.
These quasiparticles may be important in understanding the
nature of the phase transition from the antiferromagnetic state to the superconducting
state as the material is doped. In addition, the study of vortons
in high temperature superconductivity provides an interesting connection
between condensed matter physics and astrophysics/high density QCD. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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