Harmonic measure is absolutely continuous with respect to the Hausdorff measure on all low-dimensional uniformly rectifiable sets

TL;DR

This paper proves that harmonic measure is absolutely continuous with respect to Hausdorff measure on all low-dimensional uniformly rectifiable sets, removing previous topological restrictions for higher co-dimensional boundaries.

Contribution

It extends the absolute continuity result of harmonic measure to all low-dimensional uniformly rectifiable sets without topological or dimensional restrictions.

Findings

Harmonic measure is absolutely continuous with respect to Hausdorff measure on low-dimensional uniformly rectifiable sets.

No topological or dimensional restrictions are needed for these results.

The results apply to degenerate elliptic operators on such sets.

Abstract

It was recently shown that the harmonic measure is absolutely continuous with respect to the Hausdorff measure on a domain with an $n-1$ dimensional uniformly rectifiable boundary, in the presence of now well understood additional topological constraints. The topological restrictions, while mild, are necessary, as the counterexamples of C. Bishop and P. Jones show, and no analogues of these results have been available for higher co-dimensional sets. In the present paper we show that for any $d<n-1$ and for any domain with a $d$-dimensional uniformly rectifiable boundary the elliptic measure of an appropriate degenerate elliptic operator is absolutely continuous with respect to the Hausdorff measure of the boundary. There are no topological or dimensional restrictions contrary to the aforementioned results.