Solyanik estimates in ergodic theory

Abstract

Let $U_1,\dots ,U_n$ be a collection of commuting measure preserving transformations on a probability space $(\Omega ,\Sigma ,\mu )$. Associated with these measure preserving transformations is the ergodic strong maximal operator ${\mathsf{M}}_{\mathsf{S}}^{\ast }$ given by \[ \mathsf M ^\ast _{\mathsf S} f(ω) := \sup_{0 \in R \subset \mathbb{R}^n}\frac{1}{\#(R \cap \mathbb{Z}^n)}\sum_{(j_1, \ldots, j_n) \in R\cap \mathbb{Z}^n}\big|f(U_1^{j_1}\cdots U_n^{j_n}ω)\big|, \] where the supremum is taken over all open rectangles in ${\mathbb{R}}^n$ containing the origin whose sides are parallel to the coordinate axes. For $0<\alpha <1$ we define the sharp Tauberian constant of ${\mathsf{M}}_{\mathsf{S}}^{\ast }$ with respect to $\alpha$ by \[ \mathsf C ^\ast _{\mathsf S} (α) := \sup_{\substack{E \subset Ω\\ μ(E) > 0}}\frac{1}{μ(E)}μ(\{ω\in Ω: \mathsf M ^\ast _{\mathsf S} χ_E (ω) > α\}). \] Motivated by previous work of A. A. Solyanik and the authors regarding Solyanik estimates for the geometric strong maximal operator in harmonic analysis, we show that the Solyanik estimate \[ \lim_{α\rightarrow 1}\mathsf C ^\ast _{\mathsf S}(α) = 1 \] holds, and that in particular we have \[\mathsf C ^\ast _{\mathsf S}(α) - 1 \lesssim_n (1 - \frac{1}α)^{1/n}\] provided that $\alpha$ is sufficiently close to $1$. Solyanik estimates for centered and uncentered ergodic Hardy-Littlewood maximal operators associated with $U_1,\dots ,U_n$ are shown to hold as well. Further directions for research in the field of ergodic Solyanik estimates are also discussed.