Abstract
We investigate systematically the quark-hadron mixed phase in dense stellar matter, and its influence on compact star structures. The properties of quark matter and hadronic matter are fixed based on various model predictions. Beside adopting constant values, the surface tension $\Sigma$ for the quark-hadron interface is estimated with the multiple reflection expansion method and equivparticle model. To fix the structures of quark-hadron pasta phases, a continuous dimensionality of the structure is adopted as proposed by Ravenhall, Pethick, and Wilson. The corresponding properties of hybrid stars are then obtained and confronted with pulsar observations. It is found that the correlation between radius and tidal deformability in traditional neutron stars preserves in hybrid stars. For those permitted by pulsar observations, in almost all cases the quark phase persists inside the most massive compact stars. The quark-hadron interface plays an important role on hybrid star structures once quark matter emerges. The surface tension $\Sigma$ estimated with various methods increases with density, which predicts stiffer EOSs for the quark-hadron mixed phase and increases the maximum mass of hybrid stars. The EOSs of hybrid star matter are well constrained at densities $n\lesssim 0.8$ fm${}^{-3}$, while larger uncertainty is expected at higher densities.
Highlights
Due to the asymptotic freedom of strong interaction, the deconfinement phase transition is expected as one increases the density of hadronic matter
We adopt 46 equation of states (EOSs) predicted by equivparticle model [50,51,52], perturbation model [44,53,54], and Nambu-Jona-Lasinio (NJL) model [55,56]
The energy contribution due to the quark-hadron interface is treated with a surface tension Σ, for which we employ constant values as well as those estimated by the multiple reflection expansion method [58,59,60,61] and equivparticle model including both linear confinement and leading-order perturbative interactions [62,63]
Summary
Due to the asymptotic freedom of strong interaction, the deconfinement phase transition is expected as one increases the density of hadronic matter. By adopting the covariant density functional TW99 [43] for nuclear matter and perturbation model [44] for quark matter, it was found that varying the surface tension value will have sizable effects on the radii and tidal deformabilities of 1.36-solar-mass hybrid stars. Even though the perturbation model gives reliable predictions at ultrahigh densities [46], the properties of quark matter inside hybrid stars are poorly constrained Under such circumstances, in the present work, we further extend our study by investigating systematically the hadron-quark deconfinement phase transition in dense stellar matter, where various combinations of models that describe QM and HM are adopted along with different values of surface tension.
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