Global gradient estimates for Dirichlet problems of elliptic operators with a BMO antisymmetric part

Let n >= 2 and Omega subset of R-n be a bounded nontangentially accessible domain. In this article, the authors investigate (weighted) global gradient estimates for Dirichlet boundary value problems of second-order elliptic equations of divergence form with an elliptic symmetric part and a BMO antisymmetric part in Omega. More precisely, for any given p is an element of (2, infinity), the authors prove that a weak reverse Holder inequality with exponent p implies the global W-1,W-p estimate and the global weighted W-1,W-q estimate, with q is an element of [2, p] and some Muckenhoupt weights, of solutions to Dirichlet boundary value problems. As applications, the authors establish some global gradient estimates for solutions to Dirichlet boundary value problems of second-order elliptic equations of divergence form with small BMO symmetric part and small BMO antisymmetric part, respectively, on bounded Lipschitz domains, quasi-convex domains, Reifenberg flat domains, C-1 domains, or (semi-)convex domains, in weighted Lebesgue spaces. Furthermore, as further applications, the authors obtain the global gradient estimate, respectively, in (weighted) Lorentz spaces, (Lorentz-) Morrey spaces, (Musielak-)Orlicz spaces, and variable Lebesgue spaces. Even on global gradient estimates in Lebesgue spaces, the results obtained in this article improve the known results via weakening the assumption on the coefficient matrix.