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arXiv 0808.0953nucl-th
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因果耗散流体力学对相对论性重离子碰撞的适用性

The applicability of causal dissipative hydrodynamics to relativistic heavy ion collisions

Pasi Huovinen, Denes Molnar

摘要:

我们利用非平衡协变输运理论来确定因果Israel-Stewart耗散流体力学(IS)和Navier-Stokes理论(NS)的相对论重离子物理应用的有效性区域。在0+1D Bjorken方案中考虑了具有2->2相互作用的无质量理想气体,适合于碰撞的早期纵向膨胀阶段。在剪切粘度与熵密度之比η/s ~ const为常数的标度不变情况下,我们发现,如果初始膨胀时间尺度超过输运平均自由程τ 0/τ d 0> ~2的一半,Israel-Stewart理论计算耗散效应的准确度为10%。与纳维尔-斯托克斯方程相同的精度需要大三倍的τ 0/τ d 0> ~6。另一方面,对于由恒定截面驱动的动力学,需要大约50%的τ 0/τ 0> ~3(IS)和~9(NS)。对于RHIC能量s_{NN} **(1/2)~ 100-200 GeV的典型应用,这些限制意味着当eta/s > ~0.15时,甚至Israel-Stewart方法也变得微不足道。此外,我们发现,“天真”近似Israel-Stewart理论,忽略产品的梯度和耗散量,有一个更小的范围内的适用性比Navier-Stokes方程。我们还获得了解析Israel-Stewart和Navier-Stokes解在0+1D,并提出了进一步的测试数值耗散流体动力学代码在1+1,2+1,和3+1D广义守恒定律的基础上。

英文摘要:

We utilize nonequilibrium covariant transport theory to determine the region of validity of causal Israel-Stewart dissipative hydrodynamics (IS) and Navier-Stokes theory (NS) for relativistic heavy ion physics applications. A massless ideal gas with 2->2 interactions is considered in a 0+1D Bjorken scenario, appropriate for the early longitudinal expansion stage of the collision. In the scale invariant case of a constant shear viscosity to entropy density ratio eta/s ~ const, we find that Israel-Stewart theory is 10% accurate in calculating dissipative effects if initially the expansion timescale exceeds half the transport mean free path tau0/lambda0 > ~2. The same accuracy with Navier-Stokes requires three times larger tau0/lambda0 > ~6. For dynamics driven by a constant cross section, on the other hand, about 50% larger tau0/lambda0 > ~3 (IS) and ~9 (NS) are needed. For typical applications at RHIC energies s_{NN}**(1/2) ~ 100-200 GeV, these limits imply that even the Israel-Stewart approach becomes marginal when eta/s > ~0.15. In addition, we find that the 'naive' approximation to Israel-Stewart theory, which neglects products of gradients and dissipative quantities, has an even smaller range of applicability than Navier-Stokes. We also obtain analytic Israel-Stewart and Navier-Stokes solutions in 0+1D, and present further tests for numerical dissipative hydrodynamics codes in 1+1, 2+1, and 3+1D based on generalized conservation laws.

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