Flavor Nambu Jona-Lasinio Research Articles

Influence of magnetic fields on the stability and the phase transition of quark matter in the Nambu–Jona–Lasinio model

In the presence of the external magnetic fields, we investigate the stability of quark matter as well as the phase transition in the framework of two flavor Nambu–Jona–Lasinio model. The investigation focuses on the magnetic effects with the fixed coupling constant and the running coupling constant G(B, T) depending on both magnetic field and temperature. The dynamical quark mass can be increased by strong magnetic fields and be reduced by the running coupling constant G(B, T). The baryon number density is also increased by strong magnetic fields but is weakly influenced by the running coupling constant G(B, T). Importantly, the stability can be enhanced by the magnetic fields of a proper strength. While it will be reduced by the much weaker or much stronger magnetic fields. The magnetic-field-dependence in the running coupling constant has slight effect on the stability. Finally, the phase transition and the location of critical end point for both coupling cases are numerically shown.

Spin polarization and chiral condensation in a ( 2+1 )-flavor Nambu–Jona-Lasinio model at finite temperature and baryon chemical potential

We investigate the ferromagnetic (spin polarization) condensation in (2+1) flavor Nambu Jona-Lasinio(NJL) model with non-zero current quark masses at finite temperature and density which may be relevant in the context of neutron stars. The spin polarization condensation arises due to a tensor type interaction which may be generated due to non-perturbative effects in Quantum Chromodynamics(QCD). In this investigation we have shown the interplay between chiral condensate and spin polarization condensation for different values of tensor coupling. Spin polarization in the case of 2+1 flavor is different from two flavor case because of additional F$_8$ condensate associated with $\lambda_8^f$ flavor generator. We find a non-zero value of the two spin condensates in the chirally restored phase. Beyond a certain temperature the spin polarization condensates vanish for rather large quark chemical potentials. The spin condensates affect the chiral phase transition, quark masses, and the quark dispersion relation. The spin polarization condensate appears only in the chiral restored phase for light quarks. For large enough tensor couplings, it is observed that the spin polarization condensate acts as a catalyst for chiral symmetry restoration. Thermodynamic behavior of $F_3$ and $F_8$ are found to be different and they affect the quark masses differently.

Chiral symmetry breaking, color superconductivity, and equation of state for magnetized strange quark matter

We investigate the vacuum structure of dense quark matter in strong magnetic fields at finite temperature and densities in a 3 flavor Nambu Jona Lasinio (NJL) model including the Kobayashi-Maskawa-t'Hooft (KMT) determinant term using a variational method. The method uses an explicit structure for the `ground' state in terms of quark-antiquark condensates as well as diquark condensates. The mass gap equations and the superconducting gap equations are solved self consistently and are used to compute the thermodynamic potential along with the charge neutrality conditions. We also derive the equation of state for the charge neutral strange quark matter in the presence of strong magnetic fields which could be relevant for neutron stars.

Nambu–Jona-Lasinio model with proper time regularization in a finite volume

Based on the two flavor Nambu–Jona-Lasinio (NJL) model with a proper time regularization, we used stationary wave condition (SWC) for the first time to study the influence of the finite volume effects on the chiral phase transition of quark matter at finite temperature. It is found that when the cubic volume size [Formula: see text] is larger than [Formula: see text] fm, the chiral quark condensate is indistinguishable from that at [Formula: see text]. Here, it should be noted that 500 fm is far greater than the size of QGP produced at laboratory and the lattice QCD simulation space size. It is also much larger than the previous limit size [Formula: see text] fm estimated by the commonly used anti-periodic boundary condition (APBC). We also found that when the space size [Formula: see text] is less than [Formula: see text] fm, the spontaneous symmetry breaking concept is no longer valid. In addition, we first introduce the spatial susceptibility, and through the study of the spatial susceptibility, it was revealed for the first time that the chiral phase transition caused by the finite volume effects in the non-chiral limit is a crossover.

Thermodynamical properties of strongly interacting matter in a model with explicit chiral symmetry breaking interactions

We analyse the effects of the light and strange current quark masses on the phase diagram of QCD at finite temperature and vanishing baryonic chemical potential, computing the speed of sound, the trace anomaly of the energy momentum tensor and the fluctuations and correlations of the conserved charges associated to baryonic, electric and strangeness numbers. The framework is a known extension of the three flavor Nambu Jona Lasinio model, which includes the full set of explicit chiral symmetry breaking interactions (ESB) up to the same order in large $N_c$ counting as the 't Hooft flavor mixing terms and eight quark interactions. It is shown that the ESB terms are relevant for the description of a soft region in the system's speed of sound and overall slope behavior of the observables computed. At the same time the role of the 8q interactions gets highlighted. The model extension with the Polyakov loop is considered and the results are compared to lattice QCD data.

Conversion of neutron stars to 2 + 1 flavor Nambu–Jona-Lasinio quark stars as a mechanism for gamma-ray bursts

The phase transition from a neutron star to a quark star and its relation to gamma-ray bursts are investigated. A new model: the 2 + 1 flavor Nambu–Jona-Lasinio (NJL) model with the method of proper-time regularization (PTR) is utilized for the quark phase; while the Relativistic Mean Field (RMF) theory is used for the hadronic phase. The process of phase transition is studied by considering the chemical potential, paying special attention to the phase transition point and the emergence of strange quark matter. Characteristics of compact stars are illustrated, and the energy release during the phase transition is found to be [Formula: see text] erg.

Proper time regularization and the QCD chiral phase transition

We study the QCD chiral phase transition at finite temperature and finite quark chemical potential within the two flavor Nambu–Jona-Lasinio (NJL) model, where a generalization of the proper-time regularization scheme is motivated and implemented. We find that in the chiral limit the whole transition line in the phase diagram is of second order, whereas for finite quark masses a crossover is observed. Moreover, if we take into account the influence of quark condensate to the coupling strength (which also provides a possible way of how the effective coupling varies with temperature and quark chemical potential), it is found that a CEP may appear. These findings differ substantially from other NJL results which use alternative regularization schemes, some explanation and discussion are given at the end. This indicates that the regularization scheme can have a dramatic impact on the study of the QCD phase transition within the NJL model.

SU(2)-flavor NJL couplings from polarization effect

In this work corrections to the quark Nambu-Jona-Lasinio (NJL) coupling are presented in terms of the QCD parameters by considering polarization effects in terms of a generic shape of the gluon propagator. For that, the quark field is splitted into two parts and one of them, assumed to be a weak field quark, is integrated out. The resulting determinant is expanded to the 2-nd order in quark bilinears and some of the resulting couplings are exhibited.

Vacuum structure and chiral symmetry breaking in strong magnetic fields for hot and dense quark matter

We investigate chiral symmetry breaking in strong magnetic fields at finite temperature and densities in a 3 flavor Nambu Jona Lasinio (NJL) model including the Kobayashi Maskawa t-Hooft (KMT) determinant term, using an explicit structure for the ground state in terms of quark antiquark condensates. The mass gap equations are solved self consistently and are used to compute the thermodynamic potential. We also derive the equation of state for strange quark matter in the presence of strong magnetic fields which could be relevant for proto-neutron stars. ~

Lowering the critical temperature with eight-quark interactions

Abstract It is shown that eight-quark interactions, which are needed to stabilize the ground state of the combined three flavor Nambu–Jona-Lasinio and 't Hooft Lagrangians, play also an important role in determining the critical temperature at which transitions occur from the dynamically broken chiral phase to the symmetric phase.