Color superconductivity at finite temperature in Schwinger-Dyson approach. Effect of strange quark mass on QCD phase diagram

Phase transition of the color superconducting state to the quark plasma (QGP) at finite temperature is studied using the Schwinger-Dyson (SD) method in the improved ladder approximation. We compare the Cornwall-Jackiw-Tomboulis effective potential at finite temperature for two types of the color superconductor, namely the Color-Flavor locking (CFL) state and the 2flavor superconducting (2SC) state. Despite the fact that the energy density of the CFL phase is almost twice as that of the 2SC phase for all temperature, the critical temperatures of the two phases to QGP coincide: This fact implies that the CFL phase is more fragile than the 2SC state against thermal fluctuations. Effect of the strange quark mass ms on the quark-pairing is also examined. In particular, using a simple kinematical criterion, we extract ms-dependence of the ''unlocking line'' on which the CFL phase turns into the 2SC phase. (author)