Some characterizations of the preimage of $A_{\infty}$ for the Hardy-Littlewood maximal operator and consequences

TL;DR

This paper characterizes weight functions for which the Hardy-Littlewood maximal operator's preimage belongs to the class A_infinity, showing such weights are actually in A_1, with applications including new criteria for A_1.

Contribution

It provides new characterizations of weights with maximal functions in A_infinity, including criteria involving local maximal functions and alternative forms of the Coifman-Rochberg theorem.

Findings

Weights with M w in A_infinity are in A_1

New criteria using local maximal functions m_lambda

Alternative characterization of A_1 involving (f^#)^delta and (m_lambda u)^delta

Abstract

The purpose of this paper is to give some characterizations of the weight functions $w$ such that $Mw$ is in $A_{\infty}$. We show that for those weights to be in $A_{\infty}$ ensures to be in $A_{1}$. We give a criterion in terms of the local maximal functions $m_{\lambda}$ and we present a pair of applications, among them someone similar to the Coifman-Rochberg characterization of $A_{1}$ but using functions of the form $(f^{\#})^{\delta}$ and $(m_{\lambda}u)^{\delta}$ instead of $(Mf)^{\delta}$.