Maximal Function Characterizations of Hardy Spaces Associated to Homogeneous Higher Order Elliptic Operators

TL;DR

This paper characterizes Hardy spaces linked to higher order elliptic operators using maximal functions, square functions, and area functions, extending previous results and answering open questions for a range of p-values.

Contribution

It establishes non-tangential maximal function characterizations of Hardy spaces for all p in a specific range, including the case p=1, for complex elliptic operators.

Findings

Characterization of Hardy spaces via maximal functions for p in (0, p_+(L))

Answering a question for p=1 posed by Deng et al.

Representation of Hardy spaces through square and Lusin-area functions.

Abstract

Let $L$ be a homogeneous divergence form higher order elliptic operator with complex bounded measurable coefficients and $(p_-(L),\, p_+(L))$ be the maximal interval of exponents $q\in[1,\,\infty]$ such that the semigroup $\{e^{-tL}\}_{t>0}$ is bounded on $L^q(\mathbb{R}^n)$. In this article, the authors establish the non-tangential maximal function characterizations of the associated Hardy spaces $H_L^p(\mathbb{R}^n)$ for all $p\in(0,\,p_+(L))$, which, when $p=1$, answers a question asked by Deng et al. in [J. Funct. Anal. 263 (2012), 604-674]. Moreover, the authors characterize $H_L^p(\mathbb{R}^n)$ via various versions of square functions and Lusin-area functions associated to the operator $L$.