arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1507.05166cond-mat.stat-mech
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长程系统准stationary states的广义极大熵方法

Generalized maximum entropy approach to quasi-stationary states in long range systems

Gabriele Martelloni, Gianluca Martelloni, Pierre de Buyl, Duccio Fanelli

摘要:

具有长程相互作用的系统表现出向准定态(QSS)的短时弛豫,准定态的寿命随系统尺寸的增大而增大。在范式哈密顿平均场模型(HMF)的平衡相变的预测和数值检测分离均匀(零磁化)和非均匀(非零磁化)的QSS。在前一种情况下,速度分布呈现(至少)两个大的、对称的凸块,这不能通过诉诸传统的林登-贝尔最大熵方法来自洽地解释。我们提出了一个广义的最大熵方案,占伪守恒的附加电荷,均匀动量的单粒子分布。这些后者被设置为渐近值,估计直接集成的基础弗拉索夫方程,这正式举行的热力学极限。在方法论上,我们在广义吉布斯系综的框架下操作,有时在统计量子力学中定义,其中包含无限数量的守恒电荷。理论和模拟之间的协议是令人满意的,高于和低于平衡过渡阈值。我们的新方法解决了QSS的一个先前无法访问的功能,在速度分布中的多个颠簸。

英文摘要:

Systems with long-range interactions display a short-time relaxation towards Quasi Stationary States (QSS) whose lifetime increases with the system size. In the paradigmatic Hamiltonian Mean-field Model (HMF) out-of-equilibrium phase transitions are predicted and numerically detected which separate homogeneous (zero magnetization) and inhomogeneous (nonzero magnetization) QSS. In the former regime, the velocity distribution presents (at least) two large, symmetric, bumps, which cannot be self-consistently explained by resorting to the conventional Lynden-Bell maximum entropy approach. We propose a generalized maximum entropy scheme which accounts for the pseudo-conservation of additional charges, the even momenta of the single particle distribution. These latter are set to the asymptotic values, as estimated by direct integration of the underlying Vlasov equation, which formally holds in the thermodynamic limit. Methodologically, we operate in the framework of a generalized Gibbs ensemble, as sometimes defined in statistical quantum mechanics, which contains an infinite number of conserved charges. The agreement between theory and simulations is satisfying, both above and below the out of equilibrium transition threshold. A precedently unaccessible feature of the QSS, the multiple bumps in the velocity profile, is resolved by our new approach.

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