Unusual bound states of quark matter within the Nambu–Jona-Lasinio model

Properties of dense quark matter in and out of chemical equilibrium are studied within the SU(3) Nambu–Jona-Lasinio model. In addition to the four-fermion scalar and vector terms the model includes also the six-fermion flavor mixing interaction. First we study a new form of deconfined matter, meso-matter, which is composed of an equal number of quarks and antiquarks. It can be thought of as a strongly compressed meson gas where mesons are melted into their elementary constituents, quarks and antiquarks. Strongly bound states in this quark-antiquark matter are predicted for all flavor combinations of $q\overline{q}$ pairs. The maximum binding energy reaches up to 180 MeV per $q\overline{q}$ pair for mixtures with about 70% of strange $\left(s\overline{s}\right)$ pairs. Equilibrated baryon-rich quark matter with various flavor compositions is also studied. In this case only shallow bound states appear in systems with a significant admixture (about 40%) of strange quarks (strangelets). Their binding energies are quite sensitive to the relative strengths of scalar and vector interactions. The common property of all these bound states is that they appear at high particle densities when the chiral symmetry is nearly restored. Thermal properties of meso-matter as well as chemically equilibrated strange quark matter are also investigated. Possible decay modes of these bound states are discussed.