Free boundary regularity for harmonic measures and Poisson kernels.
In this note I will describe some recent results, obtained jointly with R. Fefferman and J. Pipher [RF-K-P], on the Dirichlet problem for second-order, divergence form elliptic equations, and some work in progress with J. Pipher [K-P] on the corresponding results for the Neumann and regularity problems.
We define a class of pseudodifferential operators with symbols a(x,ξ) without any regularity assumptions in the x variable and explore their boundedness properties. The results are applied to obtain estimates for certain maximal operators associated with oscillatory singular integrals.
Our concern in this paper is to describe a class of Hardy spaces H(D) for 1 ≤ p < 2 on a Lipschitz domain D ⊂ R when n ≥ 3, and a certain smooth counterpart of H(D) on R, by providing an atomic decomposition and a description of their duals.
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