Green's function for elliptic systems: moment bounds

TL;DR

This paper derives optimal bounds for the Green's function and its derivatives for elliptic systems with variable coefficients, extending results to two dimensions and systems, with applications in stochastic homogenization.

Contribution

It provides the first optimal space-scale estimates for Green's functions of elliptic systems in all dimensions, including 2D, without scalar assumptions.

Findings

Optimal estimates for Green's function in dimensions d ≥ 3

Construction and estimates of Green's function gradient in 2D

Application to stochastic homogenization with finite range dependence

Abstract

We study estimates of the Green's function in $\mathbb{R}^d$ with $d \ge 2$, for the linear second order elliptic equation in divergence form with variable uniformly elliptic coefficients. In the case $d \ge 3$, we obtain estimates on the Green's function, its gradient, and the second mixed derivatives which scale optimally in space, in terms of the "minimal radius" $r_*$ introduced in [Gloria, Neukamm, and Otto: A regularity theory for random elliptic operators; ArXiv e-prints (2014)]. As an application, our result implies optimal stochastic Gaussian bounds in the realm of homogenization of equations with random coefficient fields with finite range of dependence. In two dimensions, where in general the Green's function does not exist, we construct its gradient and show the corresponding estimates on the gradient and mixed second derivatives. Since we do not use any scalar methods in the argument, the result holds in the case of uniformly elliptic systems as well.