Quarkyonic matter and quarkyonic stars in an extended relativistic mean field model

By combining relativistic mean field models and equivparticle models with density-dependent quark masses, we construct explicitly "a quark Fermi sea" and "a baryonic Fermi surface" to model the quarkyonic phase, where baryons with momentums ranging from zero to Fermi momentums are included. The properties of nuclear matter, quark matter, and quarkyonic matter are then investigated in a unified manner, where quarkyonic matter is more stable and energy minimization is still applicable to obtain the microscopic properties of dense matter. Three different covariant density functionals TW99, PKDD, and DD-ME2 are adopted in our work, where TW99 gives satisfactory predictions for the properties of nuclear matter in both neutron stars and heavy-ion collisions and quarkyonic transition is unfavorable. Nevertheless, if PKDD with larger slope of symmetry energy L or DD-ME2 with larger skewness coefficient J are adopted, the corresponding equations of state (EOSs) are too stiff according to both experimental and astrophysical constraints. The situation is improved if quarkyonic transition takes place, where the EOSs become softer and can accommodate various experimental and astrophysical constraints.