Vector-valued Hardy spaces in non-smooth domains

We characterize the Radon–Nikodým property of a Banach space X in terms of the existence of nontangential limits of X-valued harmonic functions u defined in a domain D ⊂ Rn, n > 2, with Lipschitz boundary and belonging to maximal Hardy spaces. This extends the same result previously known for the unit disk of C. We also prove an atomic decomposition of the Borel X-valued measures in ∂D that arise as boundary limits of X-valued harmonic functions whose non-tangential maximal function is integrable with respect to harmonic measure of ∂D. © 2006 Elsevier Inc. All rights reserved.