Viscosity coefficients for hadron and quark–gluon phases

Abstract

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 twophase 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 viscosityto-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.

Shear and bulk viscosities of the gluon plasma in a quasiparticle description

“…Nonetheless, it differs from these results as the effective quasiparticle mass (T ) entering E reflects medium effects. This was also observed in [60,61,104,105].…”

“…The results for η/s from [78,104,105], where this ansatz for τ is employed, show a slightly flatter T dependence compared with our Fit 2. However, Eq.…”

“…Equation (2) differs even formally from the previous results [60,61,[102][103][104][105]. This is because it contains the subtracted mass term [ (T ) − a] as in [72,77,101] and thus also the derivative of G 2 (T ) with respect to T and not only (T ) alone.…”

Quasiparticle theory of transport coefficients for hadronic matter at finite temperature and baryon density

“…Chen, Liu, Song, and Wang calculated the shear and bulk viscosities of weakly-coupled quark gluon plasma at finite temperature and chemical potential in [53] using a quasiparticle model with medium-dependent masses and a scalar mean field. Khvorostukhin, Toneev, and Voskresensky compared three ansatzes for the generalized bulk viscosity formula [54] of a hadron gas with medium-dependent masses and a scalar mean field; see also [55,56]. Interestingly, Khvorostukhin's quasiparticle model also included a vector (ω) mean field [54,55]; as is well known, they are important to account for repulsive forces in hadronic matter with large baryon densities.…”

“…Khvorostukhin, Toneev, and Voskresensky compared three ansatzes for the generalized bulk viscosity formula [54] of a hadron gas with medium-dependent masses and a scalar mean field; see also [55,56]. Interestingly, Khvorostukhin's quasiparticle model also included a vector (ω) mean field [54,55]; as is well known, they are important to account for repulsive forces in hadronic matter with large baryon densities. This type of model is quite relevant for studying the moderate temperature hadronic matter formed in the beam energy scan at RHIC.…”