$L^p$-improving bounds for spherical maximal operators over restricted dilation sets: radial improvement

TL;DR

This paper investigates $L^p$-improving bounds for spherical maximal operators over restricted dilation sets, revealing dimension-dependent results and sharp bounds in both high and low dimensions, with implications for fractal geometry.

Contribution

It provides a comprehensive analysis of $L^p$-improving estimates for spherical maximal operators over fractal sets, highlighting differences between high and low dimensions and introducing new geometric insights.

Findings

Complete $L^p$-improving range in dimensions $d \,\geq\, 3$

Sharp results for quasi-Assouad regular sets in 2D

High-dimensional bounds depend on Minkowski dimension

Abstract

In this paper, we study the spherical maximal operator $ M_E $ over $ E\subset [1,2]$, restricted to radial functions. In higher dimensions $ d\geq 3$, we establish a complete range of $ L^p-$improving estimates for $ M_E $. In two dimensions, sharp results are also obtained for quasi-Assouad regular sets $E$. A notable feature is that the high-dimensional results depend solely on the upper Minkowski dimension, while the two-dimensional results also involve other concepts in fractal geometry such as the Assouad spectrum. Additionally, the geometric shapes of the regions corresponding to the sharp $ L^p-$improving bounds differ significantly between the two cases.