Diffusion limit for many particles in a periodic stochastic acceleration field
The one-dimensional motion of any number $N$ of particles in the field of many independent waves (with strong spatial correlation)
is formulated as a second-order system of stochastic differential equations, driven by two Wiener processes. In the limit of vanishing particle
mass $m \to 0$, or equivalently of large noise intensity, we show that the momenta of all $N$ particles converge weakly to $N$ independent
Brownian motions, and this convergence holds even if the noise is periodic. This justifies the usual application of the diffusion equation to a family
of particles in a unique stochastic force field. The proof rests on the ergodic properties of the relative velocity of two particles in the scaling limit.
Y. Elskens and E. Pardoux.