Shear and bulk viscosities of quark matter from quark-meson fluctuations in the Nambu-Jona-Lasinio model
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We have calculated the temperature dependence of shear eta and bulk zeta viscosities of quark matter due to quark-meson fluctuations. The quark thermal width originating from quantum fluctuations of quark-pi and quark-sigma loops at finite temperature is calculated with the formalism of real-time thermal field theory. Temperature-dependent constituent-quark and meson masses and quark-meson couplings are obtained in the Nambu-Jona-Lasinio model. We found a nontrivial influence of the temperature-dependent masses and couplings on the Landau-cut structure of the quark self-energy. Our results for the ratios eta/s and zeta/s, where s is the entropy density (also determined in the Nambu-Jona-Lasinio model in the quasiparticle approximation), are in fair agreement with results of the literature obtained from different models and techniques. In particular, our result for eta/s has a minimum very close to the quantum lower bound, eta/s = 1/4 pi.