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arXiv 1304.7154nucl-th
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粒子-强子物质进出平衡

Parton-hadron matter in- and out-off equilibrium

E. L. Bratkovskaya, V. Ozvenchuk, W. Cassing, V. P. Konchakovski, O. Linnyk

备注：
8 pages, 6 figures, contribution to the 29th Winter Workshop on Nuclear Dynamics, February 3-10, 2013, Squaw Valley, California, USA
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摘要：

我们研究部分子和强子物质的剪切和体积粘度-以及电导率-作为温度$T$内的部分子强子弦动力学（PHSD）的离壳输运方法的函数。利用有限盒子中的PHSD方法，在周期边界条件下研究了处于平衡态的强子和部分子动力学系统。来自PHSD的剪切粘度与熵密度$η(T)/s(T)$的比率显示接近临界温度$T_c$的最小值（具有约0.1的值）。对于$T<T_c$，即在强子阶段，由于强子系统的相互作用率较低和自由度明显较少，$η/s$的比率随着温度的降低而快速上升。体粘度$ζ(T)$ -在弛豫时间的方法评估-被发现强烈依赖于平均场（或电位）的影响，在部分子相。我们发现，在临界温度$T_c$附近，当一致地包含PHSD的标量平均场时，比值$ζ(T)/s(T)$显著增加，这也与lQCD的计算结果一致.此外，我们提出的比例$(η+3ζ/4)/s$，这是发现依赖于非平凡的温度和一般同意的lQCD计算以及结果。在PHSD计算中，接近$T_c$的$ζ(T)/η(T)$的强最大值必须归因于PHSD中编码在准粒子质量的温度依赖性中的平均场（或势）效应，这与图中（有效）耦合$g(T)$的红外增强有关。我们还发现，无量纲的电导率随温度的比值$σ_0/T$上升到$T_c$以上，近似线性地与$T$上升到$T=2.5 T_c$，但接近一个常数以上$5 T_c$，从微扰QCD（pQCD）定性预期。

英文摘要：

We study the shear and bulk viscosities of partonic and hadronic matter - as well as the electric conductivity - as functions of temperature $T$ within the Parton-Hadron-String Dynamics (PHSD) off-shell transport approach. Dynamical hadronic and partonic systems in equilibrium are studied by the PHSD simulations in a finite box with periodic boundary conditions. The ratio of the shear viscosity to entropy density $η(T)/s(T)$ from PHSD shows a minimum (with a value of about 0.1) close to the critical temperature $T_c$. For $T<T_c$, i.e. in the hadronic phase, the ratio $η/s$ rises fast with decreasing temperature due to a lower interaction rate of the hadronic system and a significantly smaller number of degrees-of-freedom. The bulk viscosity $ζ(T)$ -- evaluated in the relaxation time approach -- is found to strongly depend on the effects of mean fields (or potentials) in the partonic phase. We find a significant rise of the ratio $ζ(T)/s(T)$ in the vicinity of the critical temperature $T_c$, when consistently including the scalar mean-field from PHSD, which is also in agreement with that from lQCD calculations. Furthermore, we present the results for the ratio $(η+3ζ/4)/s$, which is found to depend non-trivially on temperature and to generally agree with the lQCD calculations as well. Within the PHSD calculations, the strong maximum of $ζ(T)/η(T)$ close to $T_c$ has to be attributed to mean-fields (or potential) effects that in PHSD are encoded in the temperature dependence of the quasiparticle masses, which is related to the infrared enhancement of the resummed (effective) coupling $g(T)$. We also find that the dimensionless ratio of the electric conductivity over temperature $σ_0/T$ rises above $T_c$ approximately linearly with $T$ up to $T=2.5 T_c$, but approaches a constant above $5 T_c$, as expected qualitatively from perturbative QCD (pQCD).

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