Tangent measures and absolute continuity of harmonic measure

Abstract

We show that for uniform domains $\\Omega\\subseteq \\mathbb R^{d+1}$ whose boundaries satisfy a certain nondegeneracy condition that harmonic measure cannot be mutually absolutely continuous with respect to $\\alpha$-dimensional Hausdorff measure unless $\\alpha\\leq d$. We employ a lemma that shows that, at almost every non-degenerate point, we may find a tangent measure of harmonic measure whose support is the boundary of yet another uniform domain whose harmonic measure resembles the tangent measure.