Nambu-Jona-Lasinio model of homogeneous neutral quark matter: Pseudoscalar diquark condensates revisited

We use a Nambu-Jona-Lasinio type model to investigate the phase diagram of dense quark matter under neutron star conditions in mean-field approximation. The model contains self-consistently determined quark masses and allows for diquark condensation in the scalar as well as in the pseudoscalar channel. The latter gives rise to the possibility of K0 condensation in the color-flavor locked phase. In agreement with earlier studies we find that this CFLK0 phase covers large regions of the phase diagram and that the predominant part of this phase is fully gapped. We show, however, that there exists a region at very low temperatures where the CFLK0 solutions become gapless, possibly indicating an instability towards anisotropic or inhomogeneous phases. The physical significance of solutions with pseudoscalar diquark condensates in the 2SC phase is discussed as well.