Variable Muckenhoupt $A_\infty$ Weights

TL;DR

This paper develops a comprehensive theory of variable Muckenhoupt $A_ty$ weights, including scalar and matrix cases, establishing reverse Hölder inequalities and characterizations in variable exponent spaces.

Contribution

It introduces variable scalar and matrix $A_ty$ weights, characterizes them via minimal operators, and proves reverse Hölder inequalities with explicit constants.

Findings

Characterization of $ ext{A}_{p( ext{·}), ext{∞}}$ weights via $p( ext{·})$-th powers.

Establishment of reverse Hölder inequalities for these weights.

Introduction of upper and lower dimensions for matrix weights and sharp estimates.

Abstract

In this article, with introducing concepts of variable scalar $\mathcal{A}_{p(\cdot),\infty}$ weights and variable matrix $\mathscr{A}_{p(\cdot),\infty}$ weights, we seek a comprehensive theory of $A_\infty$ weights within the framework of variable exponent spaces. We first show that a weight belongs to $\mathcal{A}_{p(\cdot),\infty}$ if and only if its $p(\cdot)$-th power is an $A_\infty$ weight. Using this, we characterize the $\mathcal{A}_{p(\cdot),\infty}$ condition by the minimal operator. Then we establish the reverse H\"older's inequality for $\mathcal{A}_{p(\cdot),\infty}$ weights in variable Lebesgue spaces with explicit constants and, combining this with the previously established relationship between $\mathcal{A}_{p(\cdot),\infty}$ weights and $A_\infty$ weights, we prove that, for any weight $w$, the reverse H\"older's inequality holds in variable Lebesgue spaces if and only if $w$ is an $\mathcal{A}_{p(\cdot),\infty}$ weight. For the matrix $\mathscr{A}_{p(\cdot),\infty}$ weights, we first show the existence of the reducing operators for matrix $\mathscr{A}_{p(\cdot),\infty}$ weights and then, combining the matrix $\mathscr{A}_{p(\cdot),\infty}$ weights with the scalar $\mathcal{A}_{p(\cdot),\infty}$ weights, we establish the reverse H\"older's inequality for $\mathscr{A}_{p(\cdot),\infty}$ weights in variable Lebesgue spaces. Finally, for further applications to variable matrix-weighted function spaces, we introduce the upper and the lower dimensions for $\mathscr{A}_{p(\cdot),\infty}$ weights and use these concepts to establish the sharp estimate involving reducing operators.