The maximal mean equicontinuous factor via regional mean sensitivity

TL;DR

This paper introduces the regional mean sensitive relation to better understand the maximal mean equicontinuous factor in actions of non-Abelian groups, extending previous concepts limited to Abelian groups.

Contribution

It proposes the regional mean sensitive relation as a new tool to analyze mean equicontinuity in non-Abelian group actions, overcoming limitations of earlier weak sensitivity notions.

Findings

Regional mean sensitive relation captures dynamical behavior more precisely.

Mean equicontinuity corresponds to the absence of non-diagonal regional mean sensitive pairs.

Applicable to actions of $\sigma$-compact, locally compact amenable groups.

Abstract

For actions of amenable groups, mean equicontinuity-a natural relaxation of equicontinuity obtained by averaging metrics along orbits-is well known to yield a maximal mean equicontinuous factor. In 2021, Li and Yu introduced the notion of weak sensitivity in the mean for actions of $\mathbb{Z}$ to gain a deeper understanding of this phenomenon, building on earlier work by Qiu and Zhao. We demonstrate that this relation is insufficient for actions of non-Abelian groups. To overcome this limitation, we introduce the regional mean sensitive relation, which more precisely captures the dynamical behaviour underlying the maximal mean equicontinuous factor. We discuss its fundamental properties and highlight its advantages in the non-Abelian setting. In particular, we show that mean equicontinuity is equivalent to the nonexistence of non-diagonal regional mean sensitive pairs. For this, we work in the context of actions of $\sigma$-compact and locally compact amenable groups.