Chiral spiral induced by a strong magnetic field

We study the modification of the chiral phase structure of QCD due to an external magnetic field. We first demonstrate how the effect of magnetic field can systematically be incorporated into a generalized Ginzburg-Landau framework. We then analyze the phase structure in the vicinity of the chiral critical point. In the chiral limit, the effect is found to be so drastic that it totally washes the tricritical point out of the phase diagram, bringing the continent for the chiral spiral. This is the case no matter how small is the intensity of the magnetic field. On the other hand, the current quark mass protects the chiral critical point from a weak magnetic field. However the critical point will eventually be covered by the chiral spiral phase as the magnetic field grows.Comment: 6 pages, 6 eps figures. Presented at QCD@Work 2016: International Workshop on QCD - Theory and Experiment, June 27-30, Martina-Franca (Italy

Ginzburg-Landau phase diagram of QCD near chiral critical point - chiral defect lattice and solitonic pion condensate -

We investigate the influence of the isospin asymmetry on the phase structure of quark matter near the chiral critical point systematically using a generalized version of Ginzburg-Landau approach. The effect has proven to be so profound that it brings about not only a shift of the critical point but also a rich variety of phases in its neighborhood. In particular, there shows up a phase with spatially varying charged pion condensate which we name the "solitonic pion condensate" in addition to the "chiral defect lattice" where the chiral condensate is partially destructed by periodic placements of two-dimensional wall-like defects. Our results suggest that there may be an island of solitonic pion condensate in the low temperature and high density side of QCD phase diagram.Comment: 5 pages, 4 eps figures; v2: version accepted for publication in PL

Polyakov-Nambu-Jona Lasinio model and Color-Flavor-Locked phase of QCD

The effect of Polyakov loop on the QCD phase diagram at high density is studied within the Nambu-Jona Lasinio model with Polyakov loop (PNJL model). We point out that the color neutrality is missing in the standard PNJL model at finite density. Moreover, we discuss how the color-flavor locked (CFL) phase is to be distorted by the inclusion of Polyakov loop.Comment: 6 pages, 3 eps figures; invited talk at the YITP international symposium on ``Fundamental Problems in Hot and/or Dense QCD'', Kyoto, Japan, 3-6 Mar 200

Improved Schwinger-Dyson approach to pairing phenomena and QCD phase diagram

Phase structure and phase transitions in dense QCD are studied using the Cornwall-Jackiw-Tomboulis (CJT) potential in the improved ladder approximation. The gap function, the condensation energy and the structure of Cooper pairs are investigated at finite temperature and density. Due to strong coupling effects at low densities, the gap, critical temperature and their ratio deviate from the weak coupling values. It is shown that the internal structure of Cooper pairs are robust against the thermal effects, despite the fact that the pairs are strongly correlated near the critical temperature. Also, the effect of the strange quark mass, Ms on the phase diagram is examined using a simple kinematical criterion. We discuss the behavior of the unlocking line, on which the CFL turns into the 2SC, through the variation of Ms.Comment: Talk given at the Workshop on ``Finite Density QCD at Nara'', Nara, Japan, 10-12 July 200

Thermal unpairing transitions affected by neutrality constraints and chiral dynamics

We discuss the phase structure of homogeneous quark matter under the charge neutrality constraints, and present a unified picture of the thermal unpairing phase transitions for a wide range of the quark density. We supplement our discussions by developing the Ginzburg-Landau analysis.Comment: 3 pages, 3 plots, contributed to the Proceedings of PANIC'05 (Particles and Nuclei International Conference), Santa Fe, NM, 24-28 October 200

Role of Strange Quark Mass in Pairing Phenomena in QCD

We study the dynamical effect of strange quark mass as well as kinematical one on the color-flavor unlocking transition using a NJL model. Paying a special attention to the multiplicity of gap parameters, we derive an exact formula of the effective potential for 5-gap parameters. Based on this, we discuss that the unlocking transition might be of second order rather than of first order as is predicted by a simple kinematical criterion for the unlocking.Comment: 10 pages, talk at the KIAS-APCTP International Symposium on Astro-Hadron Physics "Compact Stars: Quest for New States of Dense Matter

Gauge dynamics in the PNJL model: Color neutrality and Casimir scaling

We discuss a gauge-invariant prescription to take the mean-field approximation self-consistently in the PNJL model (Nambu--Jona-Lasinio model with the Polyakov loop). We first address the problem of non-vanishing color density in normal quark matter, which is an artifact arising from gauge-fixed treatment of the Polyakov loop mean-fields. We then confirm that the gauge average incorporated in our prescription resolves this problem and ensures color neutrality. We point out that the proposed method has an advantage in computing the expectation value of any function of the Polyakov loop matrix. We discuss the Casimir scaling as an immediate application of the method.Comment: 13 pages, 5 eps figures; v2: published versio