Sparse bounds for spherical maximal functions

By Michael T. Lacey. Journal d'Analyse Mathematique, 2017

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We consider the averages of a function f on ℝn over spheres of radius 0 < r < ∞ given by Arf(x)=Sn1f(xry)d(y)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${A_r}f(x) = \int_{{\mathbb{S}^{n - 1}}} {f(x - ry)d\sigma (y)} $$\end{document}, where σ is the normalized rotation invariant measure on 𝕊n−1. We prove a sharp range of sparse bounds for two maximal functions, the first the lacunary spherical maximal function, and the second the full maximal function. M1acf=supjZA2jf,Mfullf=supr>0Arf.\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${M_{1ac}}f = \mathop {\sup }\limits_{j \in \mathbb{Z}} {A_{{2^j}}}f,\;\;\;{M_{\text{full}}}f = \mathop {\sup }\limits_{r > 0} {A_r}f.$$\end{document} The sparse bounds are very precise variants of the known Lp bounds for these maximal functions. They are derived from known Lp-improving estimates for the localized versions of these maximal functions, and the indices in our sparse bound are sharp. We derive novel weighted inequalities for weights in the intersection of certain Muckenhoupt and reverse Hölder classes.

Subfields: Applied Mathematics, Numerical Analysis

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