Connections between the topology of the Morse boundary, the Morse local-to-global property and acylindrical hyperbolicity

TL;DR

This paper explores the relationship between Morse boundary topology, local-to-global properties, and acylindrical hyperbolicity, introducing new tools and examples in geometric group theory.

Contribution

It establishes equivalences between Morse boundary compactness and local-to-global properties, and constructs the first example of a Morse local-to-global group with specific hyperbolic features.

Findings

A group has σ-compact Morse boundary iff it is Morse local-to-global.

Introduces tools to determine Morse local-to-global property in groups.

Constructs a non-virtually cyclic Morse local-to-global group with an infinite-order Morse element not acylindrically hyperbolic.

Abstract

We relate the topology of the Morse boundary of a group to geometric and algorithmic properties of the group. In particular, we show that a group has $\sigma$-compact Morse boundary if and only if it is Morse local-to-global. We also provide tools such as the geodesic Morse local-to-global property to show that groups are (not) Morse local-to-global. Our strategy generalizes tools from small cancellation theory, such as the intersection of relators, to arbitrary finitely generated groups. Further, we introduce a class of groups akin to graded small-cancellation groups and show that, for groups in this class, a geodesic is Morse if and only if its intersection with relators grows sublinearly in the length of the relators. We use this to construct the first example of a non-virtually cyclic Morse local-to-global group with an infinite-order Morse element that is not acylindrically hyperbolic.