Flag Hardy spaces and Marcinkiewicz multipliers on the Heisenberg group: an expanded version

TL;DR

This paper develops a new theory of flag Hardy spaces on the Heisenberg group to handle Marcinkiewicz multipliers and singular integrals, bridging gaps left by classical Hardy space theory for 0<p≤1.

Contribution

Introduces flag Hardy spaces H_{flag}^{p} on the Heisenberg group, enabling boundedness of Marcinkiewicz multipliers and singular integrals for 0<p≤1, which classical theory cannot handle.

Findings

Flag Hardy spaces are bounded under flag singular integral operators.

Dual spaces of H_{flag}^{1} and H_{flag}^{p} are characterized.

A Calderón-Zygmund decomposition and interpolation theorems are established.

Abstract

Marcinkiewicz multipliers are L^{p} bounded for 1<p<\infty on the Heisenberg group H^{n}\simeqC^{n}\timesR (D. Muller, F. Ricci and E. M. Stein) despite the lack of a two parameter group of automorphic dilations on H^{n}. This lack of dilations underlies the inability of classical one or two parameter Hardy space theory to handle Marcinkiewicz multipliers on H^{n} when 0<p\leq1. We address this deficiency by developing a theory of flag Hardy spaces H_{flag}^{p} on the Heisenberg group, 0<p\leq1, that is in a sense `intermediate' between the classical Hardy spaces H^{p} and the product Hardy spaces H_{product}^{p} on C^{n}\timesR. We show that flag singular integral operators, which include the aforementioned Marcinkiewicz multipliers, are bounded on H_{flag}^{p}, as well as from H_{flag}^{p} to L^{p}, for 0<p\leq1. We characterize the dual spaces of H_{flag}^{1} and H_{flag}^{p}, and establish a Calder\'on-Zygmund decomposition that yields standard interpolation theorems for the flag Hardy spaces H_{flag}^{p}. In particular, this recovers the L^{p} results by interpolating between those for H_{flag}^{p} and L^{2} (but regularity sharpness is lost).