Topological defects in high density QCD and other strongly interacting systems
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
... 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.