Viscosity coefficients for hadron and quark-gluon phases

The shear (η) and bulk (ζ) viscosities are calculated in a quasiparticle relaxation time approximation. The hadron phase is described within the relativistic mean-field-based model with scaled hadron masses and couplings. The quark phase is treated in terms of the heavy quark bag model fitted to the lattice data. A two-phase model allowing for the first-order phase transition from the hadron phase to the strongly coupled quark-gluon plasma is constructed by means of the Gibbs conditions. Temperature and baryon density dependence of the calculated viscosity-to-entropy ratios (η/s, ζ/s) are analyzed and compared with those obtained in other models. Special attention is paid to the behavior of viscosity coefficients near the critical temperature, from both hadron and quark-gluon side. Effects of resonance widths on viscosities and viscosity-to-entropy ratios are estimated.