arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1002.3268cond-mat.stat-mech
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长程相互作用系统动力学方程的统一描述

Kinetic equations for systems with long-range interactions: a unified description

Pierre-Henri Chavanis

摘要:

我们完成了现有的文献动力学理论的系统与长程相互作用。从BBGKY族出发,或利用投影算子技巧或拟线性理论,在忽略集体效应的情况下,可以导出一般的动力学方程。这个方程(并不为人所熟知)适用于可能空间不均匀的系统,这是特定于具有长程相互作用的系统。有趣的是,这个动力学方程的结构在广义久保关系中具有明确的物理意义。此外,这个方程对恒星系统和二维点涡采取了非常相似的形式,因此提供了这些系统的动力学理论的统一描述。如果我们假设系统是空间均匀的(或轴对称的点涡),这个方程可以简化,并减少到朗道方程(或其对应的点涡)。因此,我们的形式主义提供了一个简单的推导朗道型方程。我们还使用这种一般的形式主义,推导出一个动力学方程,写在角度作用变量,描述空间非均匀系统与长程相互作用。这个新的推导解决了我们以前的推导[P. H. Chavanis,Physica A 377,469(2007)]。最后,我们考虑了一个测试粒子的方法,并推导出一般表达式的扩散和摩擦(或漂移)系数的测试粒子在浴缸中的字段粒子的演变。我们与以前在文献中获得的表达式进行了联系。作为动力学理论的一个应用,我们认为,非均匀(或高维)系统的弛豫时间短于均匀(或低维)系统,因为有潜在的更多的共振。

英文摘要:

We complete the existing literature on the kinetic theory of systems with long-range interactions. Starting from the BBGKY hierarchy, or using projection operator technics or a quasilinear theory, a general kinetic equation can be derived when collective effects are neglected. This equation (which is not well-known) applies to possibly spatially inhomogeneous systems, which is specific to systems with long-range interactions. Interestingly, the structure of this kinetic equation bears a clear physical meaning in terms of generalized Kubo relations. Furthermore, this equation takes a very similar form for stellar systems and two-dimensional point vortices providing therefore a unified description of the kinetic theory of these systems. If we assume that the system is spatially homogeneous (or axisymmetric for point vortices), this equation can be simplified and reduces to the Landau equation (or its counterpart for point vortices). Our formalism thus offers a simple derivation of Landau-type equations. We also use this general formalism to derive a kinetic equation, written in angle-action variables, describing spatially inhomogeneous systems with long-range interactions. This new derivation solves the shortcomings of our previous derivation [P.H. Chavanis, Physica A 377, 469 (2007)]. Finally, we consider a test particle approach and derive general expressions for the diffusion and friction (or drift) coefficients of a test particle evolving in a bath of field particles. We make contact with the expressions previously obtained in the literature. As an application of the kinetic theory, we argue that the relaxation time is shorter for inhomogeneous (or high-dimensional) systems than for homogeneous (or low-dimensional) systems because there are potentially more resonances.

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