论文标题
ZPC Parton Cascade的验证和改进
Validation and improvement of the ZPC parton cascade inside a box
论文作者
论文摘要
Boltzmann方程的级联解决方案在大密度和/或散射横截面处遭受因果关系的侵犯。尽管粒子细分技术可以减少因果关系的侵犯，但它会改变事件的相关性和波动，并且在计算上也很昂贵。在这里，我们评估，然后提高ZPC Parton Cascade的准确性，用于在不使用Parton细分的情况下在盒子内部的弹性散射。我们首先测试不同的碰撞方案，以解决碰撞时间和订购时间，并发现默认碰撞方案不能准确地描述大不相不良的平衡动量分布。然后，我们找到了一个特定的碰撞方案，该方案可以非常准确地描述平衡动量分布以及朝平衡的时间演变，即使在较大的不相处也是如此。我们还计算了Parton Systems的剪切粘度和$η/S $比率，并确认新的碰撞方案更准确。此外，我们使用一种新型的Parton细分方法来获得系统的“精确”演变。这种细分方法对于此类框计算有效，并且比标准细分方法更有效，我们在本研究中使用了$ 10^6 $的细分系数。
Cascade solutions of the Boltzmann equation suffer from causality violation at large densities and/or scattering cross sections. Although the particle subdivision technique can reduce the causality violation, it alters event-by-event correlations and fluctuations and is also computationally expensive. Here we evaluate and then improve the accuracy of the ZPC parton cascade for elastic scatterings inside a box without using parton subdivision. We first test different collision schemes for the collision times and ordering time and find that the default collision scheme does not accurately describe the equilibrium momentum distribution at large opacities. We then find a specific collision scheme that can describe very accurately the equilibrium momentum distribution as well as the time evolution towards equilibrium, even at large opacities. We also calculate the shear viscosity and the $η/s$ ratio of the parton systems and confirm that the new collision scheme is more accurate. In addition, we use a novel parton subdivision method to obtain the "exact" evolution of the system. This subdivision method is valid for such box calculations and is so much more efficient than the standard subdivision method that we use a subdivision factor of $10^6$ in this study.
