Interacting $ud$ and $uds$ quark matter at finite densities and quark stars

Abstract

The stability and equation of state of quark matter are studied within both two-flavor and (2+1)-flavor Nambu-Jona-Lasinio (NJL) models including the vector interactions. With a free parameter α, the Lagrangian is constructed by two parts, the original NJL Lagrangian and the Fierz transformation of it, as L = (1 − α)LNJL + αLFierz. We find that there is a possibility for both ud nonstrange and uds strange matter being absolute stable, depending on the interplay of the confinement with quark vector interaction and the exchange interaction channels. The calculated quark star properties can reconcile with the recently measured masses and radii of PSR J0030+0451 and PSR J0740+6620, as well as the tidal deformability of GW170817. Furthermore, the more strongly-interacting quark matter in the nonstrange stars allows a stiffer equation of state and consequently a higher maximum mass (∼ 2.7 M ) than the strange ones (∼ 2.1 M ). The sound velocities in strange and nonstrange quark star matter are briefly discussed compared to those of neutron star matter.

Interface effects of quark matter: $ud$QM nuggets and compact stars

“…If either SQM or udQM becomes more stable than nuclear matter, there should exist stable quark stars comprised of those matter, i.e., strange stars [11][12][13] or udQM stars [19][20][21][22][23]. For most of the cases considered here, we find that both strangelets and udQM nuggets become more stable as baryon number A increases.…”

“…Note that the gap vanishes if σ = 0, i.e., those determined by Gibbs construction in Eqs. (23)(24)(25) with the same electron chemical potentials for the uniform and nonuniform phases at the core-crust transition regions in udQM stars.…”

“…This indicates the possible existence of udQM nuggets and udQM stars, while ordinary nuclei do not necessarily decay into udQM nuggets due to a large enough surface tension [16][17][18]. Extensive investigations on the properties of nonstrange quark stars were then carried out in recent years [19][20][21][22][23].…”