Kouji Kashiwa

Entanglement between chiral and deconfinement transitions under strong uniform magnetic background field

Effects of a uniform (electro-) magnetic background field are investigated in the two-flavor nonlocal Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model. Temperature-dependences of the chiral order-parameter and the Polyakov-loop are investigated under the magnetic field. In the nonlocal PNJL model with four-dimensional momentum dependent distribution function, pseudo-critical temperatures of the chiral and deconfinement transitions are coincident each other even if the magnetic field is strong. It means that we can check the reliability of the distribution function under the strong magnetic field by comparing with lattice QCD data, particularly from the viewpoint of the entanglement between the chiral and deconfinement transitions.

Polyakov loop extended Nambu-Jona-Lasinio model with imaginary chemical potential

The Polyakov loop extended Nambu--Jona-Lasinio (PNJL) model with imaginary chemical potential is studied. The model possesses the extended

Phase diagram in the imaginary chemical potential region and extended Z{sub 3} symmetry

{\mathbb{Z}}_{3}

Critical endpoint in the Polyakov-loop extended NJL model

symmetry that QCD does. Quantities invariant under the extended

Chiral phase transition in an extended NJL model with higher-order multi-quark interactions

{\mathbb{Z}}_{3}

Evading the sign problem in the mean-field approximation through Lefschetz-thimble path integral

symmetry, such as the partition function, the chiral condensate, and the modified Polyakov loop, have Roberge-Weiss periodicity. The phase diagram of confinement/deconfinement transition derived with the PNJL model is consistent with the Roberge-Weiss prediction on it and the results of lattice QCD. The phase diagram of chiral transition is also presented by the PNJL model.

Polyakov loop and QCD thermodynamics from the gluon and ghost propagators

Phase transitions in the imaginary chemical potential region are studied by the Polyakov-loop extended Nambu-Jona-Lasinio model that possesses the extended Z{sub 3} symmetry. The extended-Z{sub 3} invariant quantities such as the partition function, the chiral condensate, and the modified Polyakov loop have the Roberge-Weiss (RW) periodicity. There appear four types of phase transitions: deconfinement, chiral, Polyakov-loop RW, and chiral RW transitions. The orders of the chiral and deconfinement transitions depend on the presence or absence of current quark mass, but those of the Polyakov-loop RW and chiral RW transitions do not. The scalar-type, eight-quark interaction newly added in the model makes the chiral transition line shift to the vicinity of the deconfinement transition line.

Determination of QCD phase diagram from the imaginary chemical potential region

Abstract The critical endpoint (CEP) and the phase structure are studied in the Polyakov-loop extended Nambu–Jona-Lasinio model in which the scalar type eight-quark ( σ 4 ) interaction and the vector type four-quark interaction are newly added. The σ 4 interaction largely shifts the CEP toward higher temperature and lower chemical potential, while the vector type interaction does oppositely. At zero chemical potential, the σ 4 interaction moves the pseudo-critical temperature of the chiral phase transition to the vicinity of that of the deconfinement phase transition.

Vector-type four-quark interaction and its impact on QCD phase structure

Abstract The chiral phase transition is studied in an extended Nambu–Jona-Lasinio model with eight-quark interactions. Equations for scalar and vector quark densities, derived in the mean field approximation, are nonlinear and mutually coupled. The scalar type nonlinear term hastens the restoration of chiral symmetry, while the scalar–vector mixing term makes the transition sharper. The scalar type nonlinear term shifts the critical endpoint toward the values predicted by lattice QCD simulations and the QCD-like theory.

Phase structure and Hosotani mechanism in gauge theories with compact dimensions revisited

The fermion sign problem appearing in the mean-field approximation is considered, and the systematic computational scheme of the free energy is devised by using the Lefschetz-thimble method. We show that the Lefschetz-thimble method respects the reflection symmetry, which makes physical quantities manifestly real at any order of approximations using complex saddle points. The formula is demonstrated through the Airy integral as an example, and its application to the Polyakov-loop effective model of dense QCD is discussed in detail.