Sharp Weak Type Estimates for Maximal Operators associated to Rare Bases

Abstract

Let $\mathcal{B}$ denote a nonempty translation invariant collection of intervals in $\mathbb{R}^n$ (which we regard as a rare basis), and define the associated geometric maximal operator $M_\mathcal{B}$ by $$M_\mathcal{B}f(x) = \sup_{x \in R \in \mathcal{B}} \frac{1}{|R|}\int_R |f|.$$ We provide a sufficient condition on $\mathcal{B}$ so that the estimate $$ |\{x \in \mathbb{R}^n : M_{\mathcal{B}}f(x) > \alpha\}|\leq C_n \int_{\mathbb{R}^{n}} \frac{|f|}{\alpha}\left(1+\log^+\frac{|f|}{\alpha}\right)^{n-1} $$ is sharp. As a corollary we obtain sharp weak type estimates for maximal operators associated to several classes of rare bases including C\'ordoba, Soria and Zygmund bases.