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arXiv 1209.5987cond-mat.stat-mech
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具有长程相互作用的流体动力学和动力学方程的线性响应理论

Linear response theory for hydrodynamic and kinetic equations with long-range interactions

Pierre-Henri Chavanis

摘要:

我们将线性响应理论应用于由流体动力学方程(如欧拉方程、Smoluchowski方程和阻尼欧拉方程)描述的具有长程相互作用的系统。我们解析地确定系统对脉冲和阶跃函数的响应。我们比较这些结果与所描述的Vlasov方程的无碰撞系统。我们表明,在线性制度,一个无碰撞的系统(弗拉索夫)的水袋分布的演变是相同的演变的碰撞为主的气体没有耗散(欧拉)。在这个类比中,水袋分布的最大速度起着相应正压气体中声速的作用。当服从阶跃函数时,这些系统表现出永久振荡。其他分布表现出朗道阻尼和松弛的稳定状态。我们用柯西分布来说明这种行为,它可以用解析的方法来研究。我们将所得结果应用于HMF模型,得到了磁化率的广义Curie-Weiss定律。最后,我们比较了线性响应理论的初始值问题的线性化Vlasov方程和报告的情况下,代数阻尼的初始扰动。

英文摘要:

We apply the linear response theory to systems with long-range interactions described by hydrodynamic equations such as the Euler, Smoluchowski, and damped Euler equations. We analytically determine the response of the system submitted to a pulse and to a step function. We compare these results with those obtained for collisionless systems described by the Vlasov equation. We show that, in the linear regime, the evolution of a collisionless system (Vlasov) with the waterbag distribution is the same as the evolution of a collision-dominated gas without dissipation (Euler). In this analogy, the maximum velocity of the waterbag distribution plays the role of the velocity of sound in the corresponding barotropic gas. When submitted to a step function, these systems exhibit permanent oscillations. Other distributions exhibit Landau damping and relax towards a steady state. We illustrate this behaviour with the Cauchy distribution which can be studied analytically. We apply our results to the HMF model and obtain a generalized Curie-Weiss law for the magnetic susceptibility. Finally, we compare the linear response theory to the initial value problem for the linearized Vlasov equation and report a case of algebraic damping of the initial perturbation.

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