Metastable quark-antiquark droplets within the Nambu–Jona-Lasinio model

Chemically nonequilibrated quark-antiquark matter is studied within the Nambu–Jona-Lasinio model. The equations of state of nonstrange $\mathrm{}(q=u,d)\mathrm{}$ and strange $\mathrm{}(q=s)\mathrm{}\hspace{0.5em}q\overline{q}$ systems are calculated in the mean-field approximation. The existence of metastable bound states with zero pressure is predicted at finite densities and temperatures $T\lesssim 50\hspace{0.5em}\mathrm{MeV}.$ It is shown that the minimum energy per particle occurs for symmetric systems, with equal densities of quarks and antiquarks. At $T=0\mathrm{}$ these metastable states have quark number densities of about $0.5\hspace{0.5em}{\mathrm{fm}}^{-3}$ for $q=u,d$ and of $1\hspace{0.5em}{\mathrm{fm}}^{-3}$ for $q=s.\mathrm{}$ A first order chiral phase transition is found at finite densities and temperatures. The critical temperature for this phase transition is approximately 75 MeV (90 MeV) for the nonstrange (strange) baryon-free quark-antiquark matter. For realistic choices of parameters, the model does not predict a phase transition in chemically equilibrated systems. Possible decay channels of the metastable $q\overline{q}$ droplets and their signatures in relativistic heavy-ion collisions are discussed.