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.

我们估计相对论强子气体中整体粘度的温度依赖性。在SMASH（模拟许多加速的强相互作用强子）中采用Green-Kubo形式主义，我们以复杂度递增的顺序研究了不同的强子系统。我们分析了单指数弛豫ansatz对整体通道相关函数的有效性，以及共振及其寿命的强烈影响。我们讨论了平衡的，长寿命系统的包容性本体粘度与短寿命混合物（如相对论重离子碰撞的强子相）的有效本体粘度之间的差异，其中反弛豫速率大于从分析中排除火球持续时间。这澄清了先前的方法之间的差异，这些方法计算的体粘度包括/排除强子气体中非常缓慢的过程。我们将最终结果与先前的强子气体计算结果进行了比较，并确认了随着温度的升高，包容性整体粘度随熵密度的下降趋势，而有效的本体粘度与熵之比虽然低于包含性，但对温度没有强烈的依赖性​​。 。