Actions of small cancellation groups on hyperbolic spaces

TL;DR

This paper constructs a rich hierarchy of group actions on hyperbolic spaces for small cancellation groups, revealing uncountably many quasi-isometry classes with specific action properties.

Contribution

It introduces a new poset of cobounded actions for small cancellation groups and demonstrates its complexity and implications for group action classifications.

Findings

Existence of a rich poset of actions with a largest element only in trivial cases

Embedding of the power set of natural numbers into the action poset

Uncountably many quasi-isometry classes with specific action properties

Abstract

We generalize Gruber--Sisto's construction of the coned--off graph of a small cancellation group to build a partially ordered set $\mathcal{TC}$ of cobounded actions of a given small cancellation group whose smallest element is the action on the Gruber--Sisto coned--off graph. In almost all cases $\mathcal{TC}$ is incredibly rich: it has a largest element if and only if it has exactly 1 element, and given any two distinct comparable actions $[G\curvearrowright X] \preceq [G\curvearrowright Y]$ in this poset, there is an embeddeding $\iota:P(\omega)\to\mathcal{TC}$ such that $\iota(\emptyset)=[G\curvearrowright X]$ and $\iota(\mathbb N)=[G\curvearrowright Y]$. We use this poset to prove that there are uncountably many quasi--isometry classes of finitely generated group which admit two cobounded acylindrical actions on hyperbolic spaces such that there is no action on a hyperbolic space which is larger than both.