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arXiv 2005.03647hep-phnucl-exnucl-th
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强子气体中的包含粘度和有效体积粘度

Inclusive and effective bulk viscosities in the hadron gas

J. -B. Rose, J. M. Torres-Rincon, H. Elfner

摘要:

我们估计了相对论性强子气体中体粘滞系数的温度依赖性。在SMASH(Simulating Many Accelerated Strongly-Interacting Hadrons)输运方法中采用Green-Kubo形式,我们研究了不同强子系统的复杂性。我们分析了体通道关联函数的单指数弛豫分析的有效性以及共振态及其寿命的强烈影响。我们讨论了一个平衡的,长寿命的系统的包容性的体积粘度之间的差异,和有效的体积粘度的相对论性重离子碰撞,其中的过程,其逆弛豫率大于火球持续时间被排除在分析的强子阶段一样,短寿命的混合物。这澄清了以前的方法之间的差异,其中计算的体积粘度,包括/不包括在强子气体中的非常缓慢的过程。我们比较我们的最终结果与以前的强子气体计算,并确认随着温度的增加,熵密度的包容性体积粘度的下降趋势,而有效的体积粘度熵比,而低于包容性的,显示没有很强的依赖于温度。

英文摘要:

We estimate the temperature dependence of the bulk viscosity in a relativistic hadron gas. Employing the Green-Kubo formalism in the SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) transport approach, we study different hadronic systems in increasing order of complexity. We analyze the (in)validity of the single exponential relaxation ansatz for the bulk-channel correlation function and the strong influence of the resonances and their lifetimes. We discuss the difference between the inclusive bulk viscosity of an equilibrated, long-lived system, and the effective bulk viscosity of a short-lived mixture like the hadronic phase of relativistic heavy-ion collisions, where the processes whose inverse relaxation rate are larger than the fireball duration are excluded from the analysis. This clarifies the differences between previous approaches which computed the bulk viscosity including/excluding the very slow processes in the hadron gas. We compare our final results with previous hadron gas calculations and confirm a decreasing trend of the inclusive bulk viscosity over entropy density as temperature increases, whereas the effective bulk viscosity to entropy ratio, while being lower than the inclusive one, shows no strong dependence to temperature.

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