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

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

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

Baryon formation and dissociation in dense hadronic and quark matter

We study the formation of baryons as composed of quarks and diquarks in hot and dense hadronic matter in a Nambu--Jona-Lasinio (NJL)--type model. We first solve the Dyson-Schwinger equation for the diquark propagator and then use this to solve the Dyson-Schwinger equation for the baryon propagator. We find that stable baryon resonances exist only in the phase of broken chiral symmetry. In the chirally symmetric phase, we do not find a pole in the baryon propagator. In the color-superconducting phase, there is a pole, but is has a large decay width. The diquark does not need to be stable in order to form a stable baryon, a feature typical for so-called Borromean states. Varying the strength of the diquark coupling constant, we also find similarities to the properties of an Efimov states.Comment: ReVTex 4, 8 pages, 7 figures; accepted version in Phys. Lett.

Thermal Phase Transitions and Gapless Quark Spectra in Quark Matter at High Density

Thermal color superconducting phase transitions in three-flavor quark matter at high baryon density are investigated in the Ginzburg-Landau (GL) approach. We constructed the GL potential near the boundary with a normal phase by taking into account nonzero quark masses, electric charge neutrality, and color charge neutrality. We found that the density of states averaged over paired quarks plays a crucial role in determining the phases near the boundary. By performing a weak coupling calculation of the parameters characterizing the GL potential terms of second order in the pairing gap, we show that three successive second-order phase transitions take place as the temperature increases: a modified color-flavor locked phase (ud, ds, and us pairings) -> a ``dSC'' phase (ud and ds pairings) -> an isoscalar pairing phase (ud pairing) -> a normal phase (no pairing). The Meissner masses of the gluons and the number of gapless quark modes are also studied analytically in each of these phases.Comment: 15 pages, 6 figure