Weakly porous sets and $A_1$ Muckenhoupt weights in spaces of homogeneous type

TL;DR

This paper characterizes sets in spaces of homogeneous type for which negative powers of their distance functions belong to the Muckenhoupt $A_1$ class, extending previous results and connecting geometric properties with weight conditions.

Contribution

It generalizes the notion of weakly porous sets and the doubling of the maximal hole function in the context of $A_1$ weights in spaces of homogeneous type.

Findings

Characterization of sets with $A_1$ weights involving negative powers of distance functions.

Extension of weak porosity concepts to spaces of homogeneous type.

Use of Whitney-type covering lemmas in the proof.

Abstract

In this work we characterize the sets $E\subset X$ for which there is some $\alpha>0$ such that the function $d(\cdot,E)^{-\alpha}$ belongs to the Muckenhoupt class $A_1(X,d,\mu)$, where $(X,d,\mu)$ is a space of homogeneous type, extending a recent result obtained by Carlos Mudarra in metric spaces endowed with doubling measures. In particular, generalizations of the notions of weakly porous sets and doubling of the maximal hole function are given and it is shown that these concepts have a natural connection with the $A_1$ condition of some negative power of its distance function. The proof presented here is based on Whitney-type covering lemmas built on balls of a particular quasi-distance equivalent to the initial quasi-distance $d$ and provided by Roberto Mac\'ias and Carlos Segovia in "A well-behaved quasi-distance for spaces of homogeneous type", Trabajos de Matem\'atica 32, Instituto Argentino de Matem\'atica, 1981, 1-18.