A generalized polar-coordinate integration formula with applications to the study of convolution powers of complex-valued functions on $\mathbb{Z}^d$

TL;DR

This paper develops a generalized polar-coordinate integration formula for positive homogeneous functions on fd4^d, and applies it to analyze convolution powers of complex-valued functions on fd4^d, providing new estimates.

Contribution

It introduces a generalized integration formula for positive homogeneous functions and applies it to convolution powers on fd4^d, extending previous results.

Findings

Established a new polar-coordinate integration formula for positive homogeneous functions.

Derived sup norm estimates for convolution powers of complex functions on fd4^d.

Extended prior results on convolution powers using the new integration framework.

Abstract

In this article, we consider a class of functions on $\mathbb{R}^d$, called positive homogeneous functions, which interact well with certain continuous one-parameter groups of (generally anisotropic) dilations. Generalizing the Euclidean norm, positive homogeneous functions appear naturally in the study of convolution powers of complex-valued functions on $\mathbb{Z}^d$. As the spherical measure is a Radon measure on the unit sphere which is invariant under the symmetry group of the Euclidean norm, to each positive homogeneous function $P$, we construct a Radon measure $\sigma_P$ on $S=\{\eta \in \mathbb{R}^d:P(\eta)=1\}$ which is invariant under the symmetry group of $P$. With this measure, we prove a generalization of the classical polar-coordinate integration formula and deduce a number of corollaries in this setting. We then turn to the study of convolution powers of complex functions on $\mathbb{Z}^d$ and certain oscillatory integrals which arise naturally in that context. Armed with our integration formula and the Van der Corput lemma, we establish sup norm-type estimates for convolution powers; this result is new and partially extends results of [20] and [21].