QCD color superconductivity in compact stars: Color-flavor locked quark star candidate for the gravitational-wave signal GW190814

At sufficiently high densities and low temperatures matter is expected to behave as a degenerate Fermi gas of quarks forming Cooper pairs, namely a color superconductor, as was originally suggested by Alford, Rajagopal, and Wilczek [Nucl. Phys. B537, 443 (1999). The ground state is a superfluid, an electromagnetic insulator that breaks chiral symmetry, called the color-flavor locked phase. If such a phase occurs in the cores of compact stars, the maximum mass may exceed that of hadronic matter. The gravitational-wave signal GW190814 involves a compact object with mass 2.6 M-circle dot, within the so-called low mass gap. Since it is too heavy to be a neutron star and too light to be a black hole, its nature has not been identified with certainty yet. Here, we show not only that a color-flavor locked quark star with this mass is viable, but also we calculate the range of the model parameters, namely the superconducting gap Delta and the bag constant B, that satisfies the strict LIGO constraints on the equation of state. We find that a color-flavor locked quark star with mass 2.6 M-circle dot satisfies the observational constraints on the equation of state if Delta >= 200 MeV and B >= 83 MeV/fm(3) for a strange quark mass m(s) = 95 MeV/c(2), and attains a radius (12.7-13.6) km and central density (7.5-9.8)10(14) g/cm(3).