Higher order elliptic and parabolic systems with variably partially BMO coefficients in regular and irregular domains

The solvability. in Sobolev spaces is proved for divergence form complex-valued higher order parabolic systems in the whole space, on a half-space, and on a Reifenberg flat domain. The leading coefficients are assumed to be merely measurable in one spacial direction and have small mean oscillations in the orthogonal directions on each small cylinder. The directions in which the coefficients are only measurable vary depending on each cylinder. The corresponding elliptic problem is also considered. (C) 2011 Elsevier Inc. All rights reserved.