Analytic capacity and dimension of sets with plenty of big projections

TL;DR

This paper advances understanding of the relationship between geometric projection properties and analytic capacity, proving new results for sets with abundant big projections and their dimensions in the plane and higher dimensions.

Contribution

It establishes that sets with plenty of big projections have positive analytic capacity and provides a quantitative lower bound, extending to higher-dimensional capacities and dimensions.

Findings

Sets with PBP have positive analytic capacity.

A lower bound for Hausdorff dimension of wiggly sets with PBP.

Estimates for capacities of subsets with PBP.

Abstract

Our main result marks progress on an old conjecture of Vitushkin. We show that a compact set in the plane with plenty of big projections (PBP) has positive analytic capacity, along with a quantitative lower bound. A higher dimensional counterpart is also proved for capacities related to the Riesz kernel, including the Lipschitz harmonic capacity. The proof uses a construction of a doubling Frostman measure on a lower content regular set, which may be of independent interest. Our second main result is the Analyst's Traveling Salesman Theorem for sets with plenty of big projections. As a corollary, we obtain a lower bound for the Hausdorff dimension of uniformly wiggly sets with PBP. The second corollary is an estimate for the capacities of subsets of sets with PBP, in the spirit of the quantitative solution to Denjoy's conjecture.