This work is devoted to the asymptotic analysis of high frequency wave propagation in random media with long-range dependence. We are interested in two asymptotic regimes, that we investigate simultaneously: the paraxial approximation, where the wave is collimated and propagates along a privileged direction of propagation, and the whitenoise limit, where random fluctuations in the background are well approximated in a statistical sense by a fractional white noise. The fractional nature of the fluctuations is reminiscent of the long-range correlations in the underlying random medium. A typical physical setting is laser beam propagation in turbulent atmosphere. Starting from the high frequency wave equation with fast non-Gaussian random oscillations in the velocity field, we derive the fractional Itô-Schrödinger equation, that is a Schrödinger equation with potential equal to a fractional white noise. The proof involves a fine analysis of the backscattering and of the coupling between the propagating and evanescent modes. Because of the long-range dependence, classical diffusion-approximation theorems for equations with random coefficients do not apply, and we therefore use moment techniques to study the convergence.where c 0 is the background velocity (constant for simplicity), and the random field V (z, x), with a stationary covariance, models fluctuations around c 0 in the slab (0, L z ) × R 2 . The parameters σ and l c represent the amplitude and the correlation length of the fluctuations. The main assumption on V is that it satisfies the long-range property in the z-direction, which is translated mathematically into a bounded non-integrable autocorrelation function which decreases at infinity only as
Preliminaries and main resultsThroughout this work, we will use the following conventions for the Fourier transform:f denotes the Fourier transform w.r.t. the variable t as in (6), andf that w.r.t. t and x, f (ω, κ) = 1 (2π) 3 f (t, x)e i(ωt+κ·x) dtdx with f (t, x) = f (ω, κ)e −i(ωt+κ·x) dωdκ.