Quasi-quark spectrum in the chiral symmetric phase from the Schwinger-Dyson equation

We non-perturbatively study the fermion spectrum in the chiral symmetric phase from the Schwinger-Dyson equation with the Feynman gauge, in which we perform an analytic continuation of the solution on the imaginary time axis to the real time axis with a method employing an integral equation. It is shown that the fermion spectrum has two peaks, which correspond to the normal quasi-fermion and the plasmino, although these peaks in the strong coupling region are very broad, owing to multiple scatterings with gauge bosons. We find that the thermal mass of the quasi-fermion saturates at some value of the gauge coupling, beyond which the thermal (pole) mass satisfies $M \sim T$, independently of the value of the gauge coupling. We also comment on the appearance of a three-peak structure in the fermion spectrum as a non-perturbative effect.Comment: 21 pages, 11 figures; This is the version published in Prog.Theor.Phy

Non-equilibrium Critical Dynamics and Precursory Phenomena in Color Superconductivity

We derive an effective equation to describe the non-equilibrium dynamics of the pair field of color superconductivity near the critical temperature. We also discuss how critical dynamics affects the specific heat and density of state above the critical temperature.Comment: 2 pages, 2 figures, PTPTeX. Proceedings of "Nuclear Matter under Extreme Conditions" at YITP, Kyoto, Japan, Dec. 1-3, 200

Further Analysis of Excitations of Quarks at Finite Temperature -- Mass Effect and Pole Structure --

We calculate the spectral function of the massive quark at finite temperature (T) using a Yukawa model and show that the peak in the negative energy region among the three-peaks found in a previous work for the massless quark is largely suppressed. To explore the underlying mechanism of this behavior, we also investigate the pole structure of the retarded Green function of the quark. We will show the result only for the massless quark. We find the residues of the poles corresponding the three-peaks are all comparable at $T\sim m_b$. We also show that the multi-peak structure of the quark spectra is well described in the pole approximation which indicates that the quasi-paricle picture is valid in this $T$ region.Comment: 6pages, 5 figures. Poster presentation at the 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (QM2006) held in Shanghai, China on November 14-20, 200

Pre-critical Phenomena of Two-flavor Color Superconductivity in Heated Quark Matter -- diquark-pair fluctuations and non-Fermi liquid behavior --

We investigate the fluctuations of the diquark-pair field and their effects on observables above the critical temperature $T_c$ in two-flavor color superconductivity (CSC) at moderate density using a Nambu-Jona-Lasinio-type effective model of QCD. Because of the strong-coupling nature of the dynamics, the fluctuations of the pair field develop a collective mode, which has a prominent strength even well above T_c. We show that the collective mode is actually the soft mode of CSC. We examine the effects of the pair fluctuations on the specific heat and the quark spectrum for T above but close to T_c. We find that the specific heat exhibits singular behavior because of the pair fluctuations, in accordance with the general theory of second-order phase transitions. The quarks display a typical non-Fermi liquid behavior, owing to the coupling with the soft mode, leading to a pseudo-gap in the density of states of the quarks in the vicinity of the critical point. Some experimental implications of the precursory phenomena are also discussed.Comment: 39 pages, 26 eps figures. The published version to appear in Prog. Theor. Phys. 114 (2005), 117-155. The references are up-date