Speaker
Description
We give a systematic account of the soft mode dynamics of QCD critical point(QCD-CP) and the two-flavor color-superconductivity(2SC-CP).
The QCD-CP of a second-order naturecomes to exist when an explicit chiral symmetry breaking is present at finite baryon density where the charge-conjugation symmetry is lost. Thus, the order parameter of it is a linear combination of the baryon density and the chiral scalar condensate, and the critical universality class is Z2, the same as that of the liquid-gas phase transition, say, of nuclear matter. Accordingly, the dynamical fluctuations of the order parameter in the normal phase has a dominant strength in the space-like region coming from the collective particle-hole excitation corresponding toden sity fluctuations; the peak energy of the collective mode goes down (softens) as the system approaches the QCD-CP in the normal phase and eventually vanishes there. This is the soft mode of the QCD-CP. We show that the photon self-energy in the medium can be greatly modified by double exciations of the soft mode by the Larkin-Aslamozov mechanism established in the metal superconductivity. Thus, quite similar physics can be applied to the soft mode assciated to the color-supercondyuctivity, provided that its phase transition is of second oeder or weak first order. In this talk, employing Nambu-Jona-Lasinio model, we show that the dilepton-pair production rate as well as the electric conductivity are anomalously enhanced near the critical points in the normal phase toward boththe 2SC and QCD-CP.