191 research outputs found

    Curvature Induced Phase Transition in a Four-Fermion Theory Using the Weak Curvature Expansion

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    Curvature induced phase transition is thoroughly investigated in a four- fermion theory with NN components of fermions for arbitrary space-time dimensions (2D<4)(2 \leq D < 4). We adopt the 1/N1/N expansion method and calculate the effective potential for a composite operator ψˉψ\bar{\psi}\psi. The resulting effective potential is expanded asymptotically in terms of the space-time curvature RR by using the Riemann normal coordinate. We assume that the space-time curves slowly and keep only terms independent of RR and terms linear in RR. Evaluating the effective potential it is found that the first-order phase transition is caused and the broken chiral symmetry is restored for a large positive curvature. In the space-time with a negative curvature the chiral symmetry is broken down even if the coupling constant of the four-fermion interaction is sufficiently small. We present the behavior of the dynamically generated fermion mass. The critical curvature, RcrR_{cr}, which divides the symmetric and asymmetric phases is obtained analytically as a function of the space-time dimension DD. At the four-dimensional limit our result RcrR_{cr} agrees with the exact results known in de Sitter space and Einstein universe.Comment: 19 pages, uses LaTeX, eepic.st

    Parameter fitting in three-flavor Nambu--Jona-Lasinio model with various regularizations

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    We study the three-flavor Nambu--Jona-Lasinio model with various regularization procedures. We perform parameter fitting in each regularization and apply the obtained parameter sets to evaluate various physical quantities, several light meson masses, decay constant and the topological susceptibility. The model parameters are adopted even at very high cutoff scale compare to the hadronic scale to study the asymptotic behavior of the model. It is found that all the regularization methods except for the dimensional one actually lead reliable physical predictions for the kaon decay constant, sigma meson mass and topological susceptibility without restricting the ultra-violet cutoff below the hadronic scale.Comment: 22 pages, 10 figure

    Phase structure of NJL model with finite quark mass and QED correction

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    We study QED corrections to the chiral symmetry breaking in Nambu-Jona-Lasinio (NJL) model with two flavors of quarks. In the model the isospin symmetry is broken by differences of the current quark masses and the electromagnetic charges between up and down quarks. In the leading order of the 1/N expansion we calculate the effective potential of the model with one-loop QED corrections. Evaluating the effective potential, we study an influence of the isospin symmetry breaking on the orientation of chiral symmetry breaking. The current quark mass has an important contribution for the orientation of chiral symmetry breaking.Comment: 7 pages, 8 figures, To appear in the proceedings of the Workshop on Origin of Mass and Strong Coupling Gauge Theories, Nagoya, Japan, 21-24 November 200