arXiv 2001.117882020-01hep-phhep-thnucl-th

强磁场中热QCD物质的动量及其输运系数

Momentum and its affiliated transport coefficients for a hot QCD matter in a strong magnetic field

Shubhalaxmi Rath, Binoy Krishna Patra

备注：: 47 pages, 7 figures
发表信息：: Phys. Rev. D 102, 036011 (2020)
DOI：: 10.1103/PhysRevD.102.036011

摘要：

我们研究了各向异性对QCD物质中剪切（$η$）和体粘（$ζ$）动量输运的影响。这些各向异性要么是由强磁场引起的，要么是由择优膨胀引起的。通过$η/s$和$ζ/s$（$s$是熵密度）的研究，可以了解物质的流动性和转捩点的位置，通过普朗特数（Pl）了解声衰减，通过雷诺数（Rl）了解流动的本质，以及了解动量扩散和电荷扩散之间的竞争。在准粒子模型内的动力学理论的弛豫时间近似中计算粘度。与各向同性介质相比，$η$和$ζ$的磁场驱动（B驱动）各向异性增加，而膨胀驱动各向异性减少。在前一种情况下，$η$随温度的增加比在后一种情况下更快，而在前一种情况下，$ζ$随温度的减少，在后一种情况下，它是贫乏的并且在特定温度下减少。因此，粘度可以区分上述各向异性。因此，$η/s$在前一种情况下得到增强，在后一种情况下，它变得小于各向同性的。类似地，$ζ/s$在强磁场中随着温度的升高而放大，但减小得更快。与各向同性相比，硼致各向异性使普朗特数增加，膨胀致各向异性使普朗特数减小。由于发现Pl大于1，所以声衰减由动量扩散控制。B驱动的各向异性使雷诺数小于1，而膨胀驱动的各向异性使其更大。比率（$\fracη{s}/\frac{σ_{\rm el}}{T}$）在B驱动的各向异性中被放大，而在膨胀驱动的各向异性中被减小。由于该比率总是大于1，因此动量扩散优于电荷扩散。

英文摘要：

We have studied the effects of anisotropies on the momentum transport in a QCD matter by shear ($η$) and bulk ($ζ$) viscosities. The anisotropies arise either by the strong magnetic field or by the preferential expansion. This study helps to understand the fluidity and location of transition point of matter through $η/s$ and $ζ/s$ ($s$ is entropy density), respectively, the sound attenuation through the Prandtl number (Pl), the nature of flow by the Reynolds number (Rl), and the competition between momentum and charge diffusions. The viscosities are calculated in the relaxation time approximation of kinetic theory within the quasiparticle model. Compared to isotropic medium, both $η$ and $ζ$ get increased in magnetic field-driven (B-driven) anisotropy, contrary to the decrease in expansion-driven anisotropy. $η$ increases with temperature faster in former case than in latter case whereas $ζ$ in former case decreases with temperature and in latter case, it is meagre and diminishes at a specific temperature. So the viscosities can distinguish aforesaid anisotropies. Thus, $η/s$ gets enhanced in former case and in latter case, it becomes smaller than isotropic one. Similarly $ζ/s$ gets amplified but decreases faster with the temperature in a strong magnetic field. The Prandtl number gets increased in B-induced anisotropy and gets decreased in expansion-induced anisotropy, compared to isotropic one. Since, Pl is found larger than 1, the sound attenuation is governed by momentum diffusion. The B-driven anisotropy makes the Reynolds number smaller than one, whereas the expansion-driven anisotropy makes it larger. The ratio ($\fracη{s}/\frac{σ_{\rm el}}{T}$) gets amplified in B-driven anisotropy whereas it gets reduced in expansion-driven anisotropy. Since, the ratio is always more than one, the momentum diffusion prevails over the charge diffusion.

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