Non-equilibrium aspects of chiral field theories
Abstract
Different aspects of the non-equilibrium chiral phase transition as well as in-medium properties of the scalar and pseudoscalar mesons is investigated using quantum field theoretical descriptions at nonzero temperatures and densities. The chiral phase transition at nonzero temperature and baryon chemical potential is studied at mean field level in the sigma model that includes quark degrees of freedom explicitly. For small bare quark masses the critical point separating the first order phase transition line and the smooth crossover region is determined. The behavior of quark and meson masses with changing temperature and chemical potential is examined. Adiabatic lines are computed showing that the critical point does not serve as focusing point in the adiabatic expansion. The linear sigma model without quarks but with field fluctuations beyond the mean field is used to derive coarse-grained equations of motion for the soft homogeneous and inhomogeneous chiral condensate fields coupled to a heath bath. Multiple effects of the heat bath on the chiral condensate fields is studied based on linear response theory. The self-consistently solved gap equation is used to determine the order of the phase transition and the temperature-dependence of meson masses. Using these masses the decay widths of pions and sigma mesons are computed at nonzero temperature at one- and two-loop order in perturbation theory. Numerical results show that in the phase transition region not only is the damping of sigma mesons significant, but also that of the pions. The in-medium modification of the pion dispersion relation is examined. A deviation at finite temperature of the velocity of massless pions from the speed of light is found. Separate investigation is carried out for the model with exact and explicitly broken chiral symmetry, making sure Goldstone's Theorem is fulfilled when chiral symmetry is spontaneously broken.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 2001
- DOI:
- 10.48550/arXiv.hep-ph/0110179
- arXiv:
- arXiv:hep-ph/0110179
- Bibcode:
- 2001PhDT........45M
- Keywords:
-
- Physics: Nuclear;
- High Energy Physics - Phenomenology
- E-Print:
- 147 pages, 31 figures, Ph. D. Thesis (advisor J. Kapusta)