自旋波的阻尼
Damping of spin waves
AI总结：
本文在理想自旋流体动力学中推导出自旋张量分量的阻尼波动方程，通过自旋-1/2费米子系统的非局域碰撞计算阻尼率，发现自旋弛豫时间可能远大于通常耗散时间尺度，表明重离子碰撞中自旋自由度在冻结时可能未达到平衡，需进行动力学处理。
摘要：
我们证明，在理想自旋流体动力学中，自旋张量的各个分量遵循阻尼波动方程。阻尼率与流体中粒子的非局域碰撞有关，这种碰撞在半经典展开中以$\hbar$的一阶项进入。该阻尼率为自旋平衡的时间尺度提供了一个估计，并通过考虑一个自旋-1/2费米子系统来计算，该系统通过四次自相互作用以及（屏蔽的）单胶子交换发生相互作用。研究发现，与系统通常的耗散时间尺度相比，自旋张量各分量的弛豫时间可以变得非常大。我们的结果表明，在重离子碰撞中，自旋自由度在冻结时刻可能并未达到平衡，因此应当对其进行动力学处理。
英文摘要：
We show that, in ideal-spin hydrodynamics, the components of the spin tensor follow damped wave equations. The damping rate is related to nonlocal collisions of the particles in the fluid, which enter at first order in $\hbar$ in a semi-classical expansion. This rate provides an estimate for the timescale of spin equilibration and is computed by considering a system of spin-1/2 fermions interacting via a quartic self-interaction as well as via (screened) one-gluon exchange. It is found that the relaxation times of the components of the spin tensor can become very large compared to the usual dissipative timescales of the system. Our results suggest that the spin degrees of freedom in a heavy-ion collision may not be in equilibrium by the time of freeze-out, and thus should be treated dynamically.
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