Local stationarity for lattice dynamics in the harmonic approximation
Abstract
Description
We consider the lattice dynamics in the harmonic approximation for We consider the lattice dynamics in the harmonic approximation for a simple hypercubic lattice with arbitrary unit cell. The initial data are random according to a probability measure which enforces slow spatial variation on the linear scale $ε^{-1}$. We establish two time regimes. For times of order $ε^{-γ}$, $0<γ<1$, locally the measure converges to a Gaussian measure which is space-time stationary with a covariance inherited from the initial (in general, non-Gaussian) measure. For times of order $ε^{-1}$ this local space covariance changes in time and is governed by a semiclassical transport equation.