We determine the strength $G_{rm v}$ of the vector-type four-quark interaction in the entanglement Polyakov-extended Nambu-Jona-Lasinio (EPNJL) model from the results of recent lattice QCD simulations with two-flavor Wilson fermions. The quark-number density is normalized by the Stefan-Boltzmann limit for small baryon chemical potential $mu$ and temperature $T$ higher than the pseudo-critical temperature $T_c$ of the deconfinement transition. The strength determined from the normalized quark-number density is $G_{rm v}=0.33 G_{rm s}$ for the strength $G_{rm s}$ of the scalar-type four-quark interaction. We explore the hadron-quark phase transition in the $mu$-$T$ plane, using the two-phase model consisting of the quantum hadrodynamics model for the hadron phase and the EPNJL model for the quark phase. When $G_{rm v}=0.33 G_{rm s}$, the critical baryon chemical potential of the transition at zero $T$ is $mu_c sim 1.6$ GeV that accounts for two solar mass measurements of neutron stars in the framework of the quark-hadron hybrid star model.
We investigate theta-vacuum effects on the QCD phase diagram for the realistic 2+1 flavor system, using the three-flavor Polyakov-extended Nambu-Jona-Lasinio (PNJL) model and the entanglement PNJL model as an extension of the PNJL model. The theta-vacuum effects make the chiral transition sharper. For large theta-vacuum angle the chiral transition becomes first order even if the quark number chemical potential is zero, when the entanglement coupling between the chiral condensate and the Polyakov loop is taken into account. We finally propose a way of circumventing the sign problem on lattice QCD with finite theta.
Nambu--Jona-Lasinio-type models have been used extensively to study the dynamics of the theory of the strong interaction at finite temperature and quark chemical potential on a phenomenological level. In addition to these studies, which are often performed under the assumption that the ground state of the theory is homogeneous, searches for the existence of crystalline phases associated with inhomogeneous ground states have attracted a lot of interest in recent years. In this work, we study the Polyakov-loop extended Nambu--Jona-Lasinio model and find that the existence of a crystalline phase is stable against a variation of the parametrization of the underlying Polyakov loop potential. To this end, we adopt two prominent parametrizations. Moreover, we observe that the existence of a quarkyonic phase depends crucially on the parametrization, in particular in the regime of the phase diagram where inhomogeneous chiral condensation is favored.
We investigate the factorization hypothesis of the four-quark condensate $langle q bar{q} q bar{q} rangle = , A , langle q bar{q} rangle^2$ with the help of the Nambu Jona-Lasinio Model supplemented with eighth order interactions. For that purpose we use the bosonization method with multiple auxiliary variables. We find that in a simplified U(1) version of the model factorization holds, whereas in the full SU(3)-flavor version of the model factorization is broken by terms which are related to the t Hooft interactions.
We investigate the three flavor Nambu-Jona Lasinio model of neutral quark matter at zero temperature and finite density, keeping into account the scalar, the pseudoscalar and the Kobayashi-Maskawa-t Hooft interactions as well as the repulsive vector plus axial-vector interaction terms (vector extended NJL, VENJL in the following). We focus on the effect of the vector interaction on the chiral restoration at finite density in neutral matter. We also study the evolution of the charged pseudoscalar meson energies as a function of the quark chemical potential.
We estimate the axion properties i.e. its mass, topological susceptibility and the self-coupling within the framework of Polyakov loop enhanced Nambu-Jona-Lasinio (PNJL) model at finite temperature and quark chemical potential. PNJL model, where quarks couple simultaneously to the chiral condensate and to a background temporal quantum chromodynamics (QCD) gauge field, includes two important features of QCD phase transition, i.e. deconfinement and chiral symmetry restoration. The Polyakov loop in PNJL model plays an important role near the critical temperature. We have shown significant difference in the axion properties calculated in PNJL model compared to the same obtained using Nambu-Jona-Lasinio (NJL) model. We find that both the mass of the axion and its self-coupling are correlated with the chiral transition as well as the confinement-deconfinement transition. We have also estimated the axion properties at finite chemical potential. Across the QCD transition temperature and/or quark chemical potential axion mass and its self-coupling also changes significantly. Since the PNJL model includes both the fermionic sector and the gauge fields, it can give reliable estimates of the axion properties, i.e. its mass and the self-coupling in a hot and dense QCD medium. We also compare our results with the lattice QCD results whenever available.
Junpei Sugano
,Junichi Takahashi
,Masahiro Ishii
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(2014)
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"Determination of the strength of the vector-type four-quark interaction in the entanglement Polyakov-extended Nambu-Jona-Lasino model"
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Junpei Sugano
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