Medium effects on the viscosities of a pion gas

Abstract

The bulk and shear viscosities of a pion gas is obtained by solving the relativistic transport equation in the Chapman-Enskog approximation. In-medium effects are introduced in the $\pi\pi$ cross-section through one-loop self-energies in the propagator of the exchanged $\rho$ and $\sigma$ mesons. The effect of early chemical freeze-out in heavy ion collisions is implemented through a temperature dependent pion chemical potential. These are found to affect the temperature dependence of the bulk and shear viscosities significantly

Bulk viscosity for pion and nucleon thermal fluctuation in the hadron resonance gas model

“…Some of them [2,4,5] indicated divergence tendency of ζ/s near transition temperature, some of effective QCD model cal-culations [22][23][24]27] revealed peak structure near transition temperature, whereas most of the effective QCD model calculations [20,21,25,27,28] as well as effective hadronic model calculations [32,[34][35][36][37], including our present work, predict a decreasing function of ζ/s(T ) in the hadronic temperature domain, with few exceptional HRG calculations [33,36]. Our decreasing ζ/s(T, µ B = 0) is representing a strongly coupled picture in the hadronic temperature domain, whose smooth extrapolation to high temperature domain agrees with a weakly coupled picture [19].…”

“…These knowledge from the earlier investigations suggest that the nature of ζ(T ) and ζ/s(T ) are still not very settled issues. Again, the numerical strength of ζ and ζ/s from different model calculations exhibit a large band -ζ ∼ 10 −5 GeV 3 [32] to 10 −2 GeV 3 [20] or, ζ/s ∼ 10 −3 [32] to 10 0 [20]. These uncertainty in nature as well as numerical values of ζ(T ) from the earlier investigations demand for further research on these kind of microscopic calculations.…”

“…These effective QCD model calculations [20][21][22][23][24][25][26][27][28] cover both QGP and hadronic phases while hadronic-model calculations of Refs. [32][33][34][35][36][37] are restricted within hadronic phase only. The present work is also addressing the estimation of ζ in the hadronic phase only.…”

“…A list of references are [2,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], where Ref. [19] addressed high temperature perturbative QCD calculations of ζ, Refs.…”

An estimate of the bulk viscosity of the hadronic medium

“…Lately, bulk viscosity of the hadronic medium has been computed in various schemes [22][23][24][25][26][27][28][29]. In this work we intend to study the role played by the phase space in deciding the bulk viscosity of the hadronic medium.…”