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微扰QCD中胶子等离子体的剪切粘度和体粘度：gg gg过程不同处理的比较<->

Shear and Bulk Viscosities of a Gluon Plasma in Perturbative QCD: Comparison of Different Treatments for the gg<->ggg Process

Jiunn-Wei Chen, Jian Deng, Hui Dong, Qun Wang

备注：
ReVTex 4, 18 pages, 7 figures, accepted version in Phys. Rev. C
发表信息：
Phys.Rev.C87(2013)024910
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摘要：

在微扰QCD中，胶子等离子体的剪切和体粘滞系数η和η的首阶贡献包括gg -&gt; gg（22）过程、gg <->ggg（23）过程和称为Landau-Pomeranchuk-Migdal（LPM）效应的多重散射过程。Arnold，Moore and Yaffe（AMY）和Arnold，Dogan and Moore（ADM）分别对η和η进行了完整的首阶计算，其中非弹性过程由有效的<->ggg胶子分裂计算。我们研究了如何互补计算与22和23过程和一个简单的处理来模拟LPM效应比较AMY和ADM的结果，我们发现，我们的结果与他们的误差范围内同意。通过研究23过程对η的贡献，我们发现在流体局域静止系中末态胶子间的最小夹角θ在θ \sim \sqrt{α_{s}}处有一个峰值分布，类似于AMY和ADM所断言的近共线分裂，但θ的平均值远大于其峰值，因为它的分布是倾斜的，有一个长尾.在质心系中，如果把23矩阵元取到软胶子韧致辐射极限，也可以看到同样的θ行为。这表明CM框架中的软胶子韧致辐射在流体局域静止框架中仍然具有某些近似共线的行为。我们还将结果推广到一般的SU（N_c）纯规范理论，并总结了目前QCD中粘滞系数的计算。

英文摘要：

The leading order contribution to the shear and bulk viscosities, ηand ζ, of a gluon plasma in perturbative QCD includes the gg -> gg (22) process, gg <-> ggg (23) process and multiple scattering processes known as the Landau-Pomeranchuk-Migdal (LPM) effect. Complete leading order computations for ηand ζwere obtained by Arnold, Moore and Yaffe (AMY) and Arnold, Dogan and Moore (ADM), respectively, with the inelastic processes computed by an effective g <-> gg gluon splitting. We study how complementary calculations with 22 and 23 processes and a simple treatment to model the LPM effect compare with the results of AMY and ADM. We find that our results agree with theirs within errors. By studying the contribution of the 23 process to η, we find that the minimum angle θamong the final state gluons in the fluid local rest frame has a distribution that is peaked at θ\sim \sqrt{α_{s}}, analogous to the near collinear splitting asserted by AMY and ADM. However, the average of θis much bigger than its peak value, as its distribution is skewed with a long tail. The same θbehavior is also seen if the 23 matrix element is taken to the soft gluon bremsstrahlung limit in the center-of-mass (CM) frame. This suggests that the soft gluon bremsstrahlung in the CM frame still has some near collinear behavior in the fluid local rest frame. We also generalize our result to a general SU(N_c) pure gauge theory and summarize the current viscosity computations in QCD.

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