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arXiv 2110.04565math.APmath-phmath.MP
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波动理论中的混沌传播与高阶顺序统计量

Propagation of chaos and the higher order statistics in the wave kinetic theory

Yu Deng, Zaher Hani

摘要:

这份手稿继续并在各个方向上扩展了arXiv:2104.11204中的结果,该结果从$d\geq 3$维的非线性薛定谔(NLS)方程中完整推导出了波动动力学方程(WKE)。波动动力学方程描述了NLS解的傅立叶模式的二阶矩在动力学时间尺度上的有效动力学,并且在动力学极限中,系统的大小发散到无穷大,并且非线性的强度根据指定的标度律渐近地消失。在这里,我们研究这些傅立叶模式的联合分布的行为,并推导出它们在动力学时间尺度上的有效极限动力学。特别是,我们证明了传播的混沌波设置:最初独立的傅立叶模式保持这种独立性的动力学限制。这些陈述是所有动力学理论的形式推导的核心,可以追溯到玻尔兹曼的工作(Stosszahlanwald)。我们通过推导高傅立叶矩的渐近性来获得这一点,高傅立叶矩是由具有因子化初始数据的波动力学层次(WKH)的解给出的。作为一个副产品,我们还提供了一个严格的理由,这种层次结构的一般(不一定是因式分解)的初始数据。我们处理高斯和非高斯初始分布。在高斯设置中,我们证明了高斯传播,因为我们表明,渐近分布保持高斯的初始数据的限制。在非高斯设置,我们推导出的高阶矩的限制方程,以及为密度函数(PDF)的解决方案。我们证明的一些结果在物理学文献中得到了证实,其他的似乎是新的。这给出了在动力学极限下的解的统计的完整描述。

英文摘要:

This manuscript continues and extends in various directions the result in arXiv:2104.11204, which gave a full derivation of the wave kinetic equation (WKE) from the nonlinear Schrödinger (NLS) equation in dimensions $d\geq 3$. The wave kinetic equation describes the effective dynamics of the second moments of the Fourier modes of the NLS solution at the kinetic timescale, and in the kinetic limit in which the size of the system diverges to infinity and the strength of the nonlinearity vanishes asymptotically according to a specified scaling law. Here, we investigate the behavior of the joint distribution of these Fourier modes and derive their effective limit dynamics at the kinetic timescale. In particular, we prove propagation of chaos in the wave setting: initially independent Fourier modes retain this independence in the kinetic limit. Such statements are central to the formal derivations of all kinetic theories, dating back to the work of Boltzmann (Stosszahlansatz). We obtain this by deriving the asymptotics of the higher Fourier moments, which are given by solutions of the wave kinetic heirarchy (WKH) with factorized initial data. As a byproduct, we also provide a rigorous justification of this hierarchy for general (not necessarily factorized) initial data. We treat both Gaussian and non-Gaussian initial distributions. In the Gaussian setting, we prove propagation of Gaussianity as we show that the asymptotic distribution retains the Gaussianity of the initial data in the limit. In the non-Gaussian setting, we derive the limiting equations for the higher order moments, as well as for the density function (PDF) of the solution. Some of the results we prove were conjectured in the physics literature, others appear to be new. This gives a complete description of the statistics of the solutions in the kinetic limit.

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