Model study of the sign problem in a mean-field approximation

We study the sign problem of the fermion determinant at nonzero baryon chemical potential. For this purpose we apply a simple model derived from Quantum Chromodynamics, in the limit of large chemical potential and mass. For SU(2) color, there is no sign problem and the mean-field approximation is similar to data from the lattice. For SU(3) color the sign problem is unavoidable, even in a mean-field approximation. We apply a phase-reweighting method, combined with the mean-field approximation, to estimate thermodynamic quantities. We also investigate the mean-field free energy using a saddle-point approximation.Comment: 7 pages, 2 figures, talk presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4, 2007, Regensburg, German

Ram-Ppressure Effects on Dense Molecular Arms in the Central Regions of Spiral Galaxies by Intracluster Medium

We investigated ram-pressure effects by an intracluster wind on an inner disk of spiral galaxies by a hydrodynamical simulation. Even if the wind is mild and not strong enough to strip the gas disk, the ram pressure disturbs orbits of the inter-arm gas significantly. This results in asymmetric dense molecular arms in the inner few kpc region of a galaxy. This mechanism would explain the asymmetric CO gas distributions in the central regions often observed in Virgo spirals.Comment: To appear in PASJ. 7 pages, 3 gif figure

Broken spacetime symmetries and elastic variables

We discuss spontaneous breaking of continuum symmetries, whose generators do explicitly depend on the spacetime coordinates. We clarify the relation between broken symmetries and elastic variables at both zero and finite temperatures, and/or finite densities, and show the general counting rule that is model-independently determined by the symmetry breaking pattern. We apply it to three intriguing examples: rotational, conformal, and gauge symmetries.Comment: 6 pages, 1 figure; some discussions added in Sec. 4, published versio

General formulae for dipole Wilson line correlators with the Color Glass Condensate

We present general formulae to compute Wilson line correlators with the Color Glass Condensate described by the McLerran-Venugopalan model. We explicitly construct a complete and non-orthogonal set of color-singlet bases and write matrix elements down, so that the exponential of the matrix leads to the Wilson line correlators. We further develop a systematic perturbative expansion of dipole Wilson line correlators in terms of $1/N_c$ where $N_c$ is the color number. As a phenomenological application we calculate the flow harmonics $v_n\{m\}$ in the dipole model and discuss the $N_c$ scaling.Comment: 19 pages, 4 figure