Local Stationarity for Lattice Dynamics in the Harmonic Approximation

#### T.V. Dudnikova, H. Spohn

2006, v.12, Issue 4, 645-678

ABSTRACT

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 $\varepsilon^{-1}$. We establish two time regimes. For times of order $\varepsilon^{-\gamma}$, $0<\gamma<1$, 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 $\varepsilon^{-1}$ this local space covariance changes in time and is governed by a semiclassical transport equation.

Keywords: harmonic crystal,random initial data,covariance matrices,weak convergence of measures,semiclassical transport equation