Annulus Maximal Averages on Variable Hyperplanes

Abstract

By giving a thin width of $0<\delta\ll 1$ to both a unit circle and a unit line, we set an annulus and a tube on the Euclidean plane $\mathbb{R}^2$. Consider the maximal means $M_\delta$ over dilations of the annulus, and $N_\delta$ over rotations of the tube. It is known that their operator norms on $L^2(\mathbb{R}^2)$ are $O(|\log 1/\delta|^{1/2})$. In this paper, we study the maximal averages $\mathcal{M}^A_\delta$ and $\mathcal{N}^A_\delta$ over those annuli and tubes now imbedded on the variable hyperplanes $(x,x_3)+\left\{\left(y, \langle A(x), y\rangle\right): y\in\mathbb{R}^2\right\}\subset \mathbb{R}^3$ where $A$ is a $2\times 2$ matrix. The model hyperplane is the horizontal plane of the Heisenberg group when $A$ is the skew--symmetric matrix denoted by $E$. It turns out that a rank of matrix $EA+(EA)^T$ or $A+A^T$ determines $\|\mathcal{M}^A_\delta\|_{op} $ or $\|\mathcal{N}^A_\delta\|_{op}$ respectively. In the higher dimension, the corresponding spherical maximal means is bounded in $L^p$ if $A$ has only complex eigenvalues.