Bounding the dimension of exceptional sets for orthogonal projections

Peter Cholak, Marianna Csornyei, Neil Lutz, Patrick Lutz, Elvira Mayordomo, D. M. Stull

Published 2024-11-07Version 1

It is well known that if $A\subseteq\R^n$ is an analytic set of Hausdorff dimension $a$, then $\dim_H(\pi_VA)=\min\{a,k\}$ for a.e. $V\in G(n,k)$, where $\pi_V$ is the orthogonal projection of $A$ onto $V$. In this paper we study how large the exceptional set \begin{center} $\{V\in G(n,k) \mid \dim_H(\pi_V A) < s\}$ \end{center} can be for a given $s\le\min\{a,k\}.$ We improve previously known estimates on the dimension of the exceptional set, and we show that our estimates are sharp for $k=1$ and for $k=n-1$.