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arXiv 0810.5670hep-ph
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审查“自下而上”设想方案

Review of the "Bottom-Up" scenario

Andrej El, Zhe Xu, Carsten Greiner

摘要:

在部分子级联BAMPS中研究了具有Bjorken增强不变几何的纵向膨胀彩色玻璃凝聚体的热化。我们的主要重点在于热化的详细比较,在BAMPS中观察到的建议在自下而上的情况。我们证明了在RHIC和LHC能区的重离子碰撞中,由于反反应$ggg\to gg$阻碍了粒子的绝对增殖,所以在Bottom-Up图中作为早期预平衡过程的主导过程的$gg \to ggg$产生的大量软胶子不会发生.此外,与自下而上的情况相反,软胶子和硬胶子同时热化。BAMPS计算中热平衡的时间尺度为$\as^{-2} (\ln \as)^{-2} Q_s^{-1}$量级。在此之后,胶子系统表现出近似流体动力学行为。剪切粘度与熵密度比对$Q_s$的依赖性较弱,接近AdS/CFT猜想的下界。

英文摘要:

Thermalization of a longitudinally expanding color glass condensate with Bjorken boost invariant geometry is investigated within parton cascade BAMPS. Our main focus lies on the detailed comparison of thermalization, observed in BAMPS with that suggested in the Bottom-Up scenario. We demonstrate that the tremendous production of soft gluons via $gg \to ggg$, which is shown in the Bottom-Up picture as the dominant process during the early preequilibration, will not occur in heavy ion collisions at RHIC and LHC energies, because the back reaction $ggg\to gg$ hinders the absolute particle multiplication. Moreover, contrary to the Bottom-Up scenario, soft and hard gluons thermalize at the same time. The time scale of thermal equilibration in BAMPS calculations is of order $\as^{-2} (\ln \as)^{-2} Q_s^{-1}$. After this time the gluon system exhibits nearly hydrodynamic behavior. The shear viscosity to entropy density ratio has a weak dependence on $Q_s$ and lies close to the lower bound of the AdS/CFT conjecture.

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