Hybrid stars using the quark-meson coupling and proper-time Nambu-Jona-Lasinio models

Background: At high density deconfinement of hadronicmattermay occur leading to quark matter. The immense densities reached in the inner core of massive neutron stars may be sufficient to facilitate the transition. Purpose: To investigate a crossover transition between two phenomenological models which epitomize quantum chromodynamics in two different regimes, while incorporating the influence of quark degrees of freedom in both. Method: We use the Hartree-Fock quark-meson coupling model and the proper-time regularized three-flavor Nambu-Jona-Lasinio model to describe hadronic and quark matter, respectively. Hybrid equations of state are obtained by interpolating the energy density as a function of total baryonic density and calculating the pressure. Results: Equations of state for hadronic, quark, and hybrid matter and the resulting mass versus radius curves for hybrid stars are shown, as well as other relevant physical quantities such as species fractions and the speed of sound in matter. Conclusions: The observations of massive neutron stars can certainly be explained within such a construction. However, the so-called thermodynamic correction arising from an interpolation method can have a considerable impact on the equation of state. The interpolation dependency of and physical meaning behind such corrections require further study.