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 approach to inhomogeneous chiral phases of QCD

We study the inhomogeneous chiral condensates in the proximity of the chiral tricritical point (TCP) of two-flavor QCD. Deriving the Ginzburg-Landau (GL) functional up to the eighth order in the order parameter and its spatial derivative, we explore off the TCP and find that critical curves are bent by non-linear effects. In the newly extend GL coupling space, we find the TCP being realized as a multicritical point where five independent critical lines meet up. We also present general analyses for the energies associated with several higher dimensional crystal structures.Comment: 5 pages, 5 eps figures. Talk presented at QCD@Work 2012: International Workshop on QCD - Theory and Experiment, June 18-21, Lecce, Ital

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

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

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

Color Superconductivity in Dense QCD and Structure of Cooper Pairs

The two-flavor color superconductivity is examined over a wide range of baryon density with a single model. To study the structural change of Cooper pairs, quark correlation in the color superconductor is calculated both in the momentum space and in the coordinate space. At extremely high baryon density, our model becomes equivalent to the usual perturbative QCD treatment and the gap is shown to have a sharp peak near the Fermi surface due to the weak-coupling nature of QCD. On the other hand, the gap is a smooth function of the momentum at lower densities due to strong color magnetic and electric interactions. The size of the Cooper pair is shown to become comparable to the averaged inter-quark distance at low densities, which indicates a crossover from BCS to BEC (Bose-Einstein condensation) of tightly bound Cooper pairs may take place at low density.Comment: 6 pages, 5 figures. Invited talk at the Joint CSSM/JHF Workshop on Physics at Japan Hadron Facility (March 14-21, Adelaide, 2002

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