133 research outputs found

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

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    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

    Broken spacetime symmetries and elastic variables

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    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

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    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/Nc1/N_c where NcN_c is the color number. As a phenomenological application we calculate the flow harmonics vn{m}v_n\{m\} in the dipole model and discuss the NcN_c scaling.Comment: 19 pages, 4 figure

    Counting rule for Nambu-Goldstone modes in nonrelativistic systems

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    The counting rule for Nambu-Goldstone modes is discussed using Mori's projection operator method in nonrelativistic systems at zero and finite temperatures. We show that the number of Nambu-Goldstone modes is equal to the number of broken charges, Q_a, minus half the rank of the expectation value of [Q_a,Q_b].Comment: 5 pages, no figures; typos corrected; some discussion added and clarifie

    Fermion Spectrum at Ultrasoft Region in a Hot QED/QCD Plasma

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    An spectrum of an electron (quark) with ultrasoft momentum (p g^2T) is discussed at extremely high temperature in quantum electrodynamics (chromodynamics) with a resummed perturbation theory. We establish the existence of the pole suggested in the previous work of the electron (quark) propagator at ultrasoft region, and find that its pole position is p_0=\mp |p|/3-i\zeta, where \zeta is the damping rate which is of order g^2T ln 1/g, and the expression of its residue. We also discuss whether the resummation scheme preserves the gauge symmetry.Comment: 3 pages, 1 figure, presented by D. Satow at the 19th Particles and Nuclei International Conference, PANIC 2011, MIT, Cambridge, MA (July 24-29, 2011
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