Visible parts and slices of Ahlfors regular sets

Abstract

We show that for any compact set $E\subset {\mathbb{R}}^d$ the visible part of $E$ has Hausdorff dimension at most $d-1/6$ for almost every direction. This improves recent estimates of Orponen and Matheus. If $E$ is $s$-Ahlfors regular, where $s>d-1$, we prove a much better estimate. In that case for almost every direction the Hausdorff dimension of the visible part is at most $s-\alpha (s-d+1),$ where $\alpha >0.183$ is absolute. The estimate is new even for self-similar sets satisfying the open set condition. Along the way, we prove a refinement of the Marstrand’s slicing theorem for Ahlfors regular sets.