热QCD：强耦合与弱耦合区间的输运系数
Hot QCD: transport coefficients in strong and weak coupling regimes
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中文总结 AI 辅助
本文在准粒子模型下，利用新型格点QCD数据首次计算热QCD的剪切黏度和重夸克扩散系数，并比较强、弱耦合区间的输运性质。
中文摘要 AI 辅助
我们在准粒子模型（QPM）框架内评估了输运系数，即剪切黏度 $\eta$ 和重夸克的空间扩散系数 $D_s$。特别是，这是首次利用 $N_f=3+1$ 的新型格点QCD（lQCD）数据来完成这一计算。在该框架中，胶子具有质量，夸克与胶子之间的相互作用通过由树级费曼图计算得到的散射矩阵进行评估。就 $D_s$ 的评估而言，我们采用相对论玻尔兹曼方程的福克-普朗克近似，用于描述粲夸克和底夸克在 $N_f=3$ 以及 $N_f=3+1$ 的介质中的扩散。我们针对夸克-胶子混合物的比值 $\eta/s$（其中 $s$ 为熵密度）发展了一种双组分查普曼-恩斯科格形式体系。剪切黏度的温度依赖性随后与基于格林-久保方法的结果进行比较，该方法基于相对论玻尔兹曼方程的数值求解，并采用碰撞积分的随机实现。最后，利用上述结果，我们比较了比值 $(2\pi T D_s)/(4\pi \eta/s)$ 的强耦合与弱耦合区间。
英文摘要
We evaluate the transport coefficients, namely the shear viscosity $η$ and the spatial diffusion coefficient of heavy quarks $D_s$, within a Quasi-Particle Model (QPM). In particular, for the first time this has been done by exploiting novel lQCD data at $N_f=3+1$. In such a framework, in which the gluons are massive, the interactions among quarks and gluons have been evaluated via the scattering matrices evaluated from tree level Feynman diagrams. As far as the evaluation of $D_s$ is concerned, the Fokker-Planck approximation for the relativistic Boltzmann equation has been employed for the diffusion of both charm and bottom quarks in either a $N_f=3$ and a $N_f=3+1$ bulk. We have developed a dual-component Chapman-Enskog formalism for the ratio $η/s$ (being $s$ the entropy density) of a mixture of quarks and gluons. The temperature dependence of the shear viscosity is then compared to the results from a Green-Kubo approach, based on the numerical resolution of the relativistic Boltzmann equation with a stochastic implementation of the collision integral. Finally, using the above results, we compare the strong and weak coupling regimes for the ratio $(2πT D_s)/(4πη/s)$.
