COLOR SUPERCONDUCTING QUARK MATTER AND COMPACT STAR OBSERVABLES

Abstract

We investigate a nonlocal chiral quark model with separable 4-fermion interac- tion for the case of U (3) flavor symmetry and show that strange quark matter is unlikely to occur in a large enough volume of a compact star to entail remark- able observational consequences. The phase diagram in the two-flavor sector of such model has a critical end point of the line of first order chiral/deconfinement phase transitions on which a triple point marks the junction with the critical line for second order phase transitions to two-flavor color superconductivity (2SC) below T ∼ 80 MeV. Stable hybrid star configurations with large quark matter core in a color superconducting phase can exist. We suggest that for accreting compact stars in Low-mass X-ray binary (LMXB) systems a population gap in the phase diagram (Ω-M plane) for rotating compact star configurations would be an observable indicator of such a quark matter core. A consistent cooling phenomenology for such hybrid stars requires that no direct Urca type fast cool- ing process in the hadronic shell occurs and that all quark species be gapped, with the minimum pairing gap being a decreasing function of the chemical po- tential in the range of 1 MeV to 10 keV. We discuss possible implications of a QCD phase transition for the early evolution of hot proto-neutron stars regard- ing delayed energy release by neutrinos and a possible gamma-ray burst (GRB) mechanism.