Abstract
We present a novel relativistic density-functional approach to modeling quark matter with a mechanism to mimic confinement. The quasiparticle treatment of quarks provides their suppression due to large quark selfenergy already at the mean-field level. We demonstrate that our approach is equivalent to a chiral quark model with medium-dependent couplings. The dynamical restoration of the chiral symmetry is ensured by construction of the density functional. Beyond the mean field, quark correlations in the pseudoscalar channel are described within the Gaussian approximation. This explicitly introduces pionic states into the model. Their contribution to the thermodynamic potential is analyzed within the Beth–Uhlenbeck framework. The modification of the meson mass spectrum in the vicinity of thee (de)confinement transition is interpreted as the Mott transition. Supplemented with the vector repulsion and diquark pairing the model is applied to construct a hybrid quark-hadron EoS of cold compact-star matter. We study the connection of such a hybrid EoS with the stellar mass-radius relation and tidal deformability. The model results are compared to various observational constraints including the NICER radius measurement of PSR J0740+6620 and the tidal deformability constraint from GW170817. The model is shown to be consistent with the constraints, still allowing for further improvement by adjusting the vector repulsion and diquark pairing couplings.
Highlights
A principal element of unified description of strongly interacting matter within e↵ective theories is the hadronization of chiral quark models and the incorporation of a confinement mechanism into them, manifesting the switching between hadronic and quark degrees of freedom
We have studied a relativistic density functional approach to quark matter, which i) mimics the quark confinement by a rapid growth of the quark self-energy in the confining region, ii) respects chiral symmetry of strong interaction and iii) can be interpreted as a chiral quark model with the density dependent coupling constants
In addition to the vector repulsion channel, we have introduced the diquark pairing not studied before within the density functional approach
Summary
A principal element of unified description of strongly interacting matter within e↵ective theories is the hadronization of chiral quark models and the incorporation of a confinement mechanism into them, manifesting the switching between hadronic and quark degrees of freedom. In the two-flavor case this introduces the pion degrees of freedom and in combination with the proposed phenomenological confinement mechanism of quarks in the chirally broken phase it provides a quark-hadron duality within our approach Another important and new aspect of this study is the introduction of the diquark pairing channels into the density functional approach. The recent analysis of observational data on the pulsar PSR J0740+6620 [4, 5] and the binary neutron star (NS) merger GW170817 [6] established challenging constraints on the mass-radius diagram of NS Fulfilling these constraints requires the EoS of stellar matter to exhibit a significant softening in the density range typical for the intermediate-mass NS with a further sti↵ening at larger densities typical for NS with masses about two times the solar mass.
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