Color Superconductivity: Phase Diagrams and Goldstone Bosons in the Color-Flavor Locked Phase

• Main Author: Kleinhaus, Verena
• Format: Others
• Language: English; en
• Published: 2009
• Online Access: https://tuprints.ulb.tu-darmstadt.de/1380/1/thesis_kleinhaus.pdf; Kleinhaus, Verena <http://tuprints.ulb.tu-darmstadt.de/view/person/Kleinhaus=3AVerena=3A=3A.html> (2009): Color Superconductivity: Phase Diagrams and Goldstone Bosons in the Color-Flavor Locked Phase.Darmstadt, Technische Universität, [Ph.D. Thesis]

The phase diagram of strongly interacting matter is studied with great experimental and theoretical effort and is one of the most fascinating research areas in modern particle physics. It is believed that color superconducting phases, in which quarks form Cooper pairs, appear at very high densities and low temperatures. Such phases could appear in the cores of neutron stars. In this work color superconducting phases are studied within the Nambu-Jona-Lasinio model. First of all, the phase diagram of neutral matter in beta equilibrium is calculated for two different diquark couplings. To this end, we determine the dynamical quark masses self-consistently together with the order parameters of color superconductivity. The interplay between neutrality and quark masses results in an interesting phase structure, in particular for the smaller diquark coupling. In the following, we additionally include a conserved lepton number to map the situation in the first few seconds of the evolution of a protoneutron star when neutrinos are trapped. This has a huge influence on the phase structure and favors the 2SC phase compared to the CFL phase. In the second part of this work we concentrate on the CFL phase which is characterized by a special symmetry breaking pattern. The properties of the resulting nine pseudoscalar Goldstone bosons (GB) are studied by solving the Bethe-Salpeter equation for quark-quark scattering. The GB are the lowest-lying excitations in the CFL phase and therefore play an important role for the thermodynamics of the system. The properties of the GB can also be described by the low-energy effective theory (LEET) for the CFL phase. There the respective low-energy constants are derived for asymptotically high densities where the strong force is weak and can be treated perturbatively. Our aim is the comparison of our results with these predictions, on the one hand to check our model in the weak-coupling limit and on the other hand to derive information about the range of validity of the weak-coupling limit at moderate densities. As expected, the GB are massless in the chiral limit. For finite but equal quark masses the GB masses grow linear with the quark mass. The eight GB related to chiral symmetry breaking are degenerate while the ninth is slightly heavier. For unequal quark masses the GB of chiral symmetry breaking are no longer degenerate, but show an inverse mass ordering where the kaons are lighter than the pions. For equal and unequal quark masses the results are in qualitative agreement with the LEET predictions. However, we find quantitative deviations from the weak-coupling limit. Furthermore, we calculate the decay constants of the GB. Our results reproduce the weak-coupling limit and again show noticeable deviations for stronger couplings.