The two-equation of state model is used to describe the hadron-quark phase transition in dense-hot matter formed in heavy-ion collisions. The nonlinear Walecka model is used to describe the hadronic phase. For the quark phase, the Nambu-Jona-Lasinio (NJL) model coupled to Polyakov-loop fields is used to include both the chiral and (de)confinement dynamics. The phase diagrams are derived from the Gibbs conditions and compared with the results obtained in the hadron-NJL model without confinement. As in the hadron-NJL case a first order transition is observed, but with a critical end point at much higher temperatures, a consequence of the confinement mechanism that reduces the degrees of freedom of the quark matter in proximity to the phase transition. Particular attention is devoted to the phase transition in isospin asymmetric matter. Interesting isospin effects are found at high baryon density and reduced temperatures, which are in fact also common to other quark models, like the MIT bag model and the NJL model. Some possible observational signals are suggested to probe in heavy-ion collision experiments at intermediate energies.
The two-Equation of State (EoS) model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the threeflavor Nambu-Jona-Lasinio (NJL) effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed current quark masses, the main important effect of the chiral dynamics is the appearance of an End-Point for the coexistence zone. We show that a first order hadron-quark phase transition may take place in the region T ⊂ (50 − 80) MeV and ρ B ⊂ (2 − 4) ρ0, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin properties of the mixed phase some possible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of Critical-End-Point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain.
The hadron-quark/gluon phase transition is studied in the two-phase model. As a further study of our previous work, both the isoscalar and isovector vector interactions are included in the Polyakov loop modified Nambu-Jona-Lasinio model (PNJL) for the quark phase. The relevance of the exchange ( Fock ) terms is stressed and suitably accounted for. The calculation shows that the isovector vector interaction delays the phase transition to higher densities and the range of the mixed phase correspondingly shrinks. Meanwhile the asymmetry parameter of quark matter in the mixed phase decreases with the strengthening of this interaction channel. This leads to some possible observation signals being weakened, although still present. We show that these can be rather general effects of a repulsion in the quark phase due to the symmetry energy. This is also confirmed by a simpler calculation with the MIT-Bag model. However, the asymmetry parameter of quark matter is slightly enhanced with the inclusion of the isoscalar vector interaction, but the phase transition will be moved to higher densities. The largest uncertainty on the phase transition lies in the undetermined coupling constants of the vector interactions. In this respect new data on the mixed phase obtained from Heavy Ion Collisions at Intermediate Energies appear very important.
The hadron-quark phase transition in the core of massive neutron stars is studied with a newly constructed two-phase model. For nuclear matter, a nonlinear Walecka type model with general nucleon-meson and meson-meson couplings, recently calibrated by Steiner, Hemper and Fischer, is taken. For quark matter, a modified Polyakov-Nambu-Jona-Lasinio (mPNJL) model, which gives consistent results with lattice QCD data, is used. Most importantly, we introduce an isoscalar-vector interaction in the description of quark matter, and we study its influence on the hadron-quark phase transition in the interior of massive neutron stars. With the constraints of neutron star observations, our calculation shows that the isoscalar-vector interaction between quarks is indispensable if massive hybrids star exist in the universe, and its strength determines the onset density of quark matter, as well as the mass-radius relations of hybrid stars. Furthermore, as a connection with heavy-ioncollision experiments we give some discussions about the strength of isoscalar-vector interaction and its effect on the signals of hadron-quark phase transition in heavy-ion collisions, in the energy range of the NICA at JINR-Dubna and FAIR at GSI-Darmstadt facilities.
The Poyakov-Nambu-Jona-Lasinio (PNJL) model was developed recently, which includes both the chiral dynamics and (de)confinement effect and gives a good description of lattice QCD data. In this study we use the PNJL model to describe the quark phase, and first use it to study the evolution of proto-neutron star (PNS) with a hadron-quark phase transition. Along the line of a PNS evolution, we take several snapshots of PNS profiles, presenting the fractions of different species, the equations of state (EOS), and the mass-radius relations at different stages. The calculation shows the mixed phase may exist during the whole evolving process, and the onset density of quark phase decreases with the radiation of neutrinos in the heating stage. In the cooling stage, the EOS of the mixed phase softens and the center density increases. In this process a part of nuclear matter transforms to quark matter, which may lead to a PNS collapsing into a black hole.
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