Rigidity phenomena and the statistical properties of group actions on $\text{CAT}(0)$ cube complexes

TL;DR

This paper investigates the relationship between the marked length spectra of certain group actions on CAT(0) cube complexes, establishing conditions under which these spectra are homothetic and analyzing associated geometric curves.

Contribution

It introduces a finite-state automaton encoding the spectra of pairs of cubulations and applies thermodynamic formalism to derive new properties of the Manhattan curve and length spectra.

Findings

The Manhattan curve is analytic and convex.

The curve is a straight line if and only if spectra are homothetic.

A large deviation theorem for length spectra is proved.

Abstract

We compare the marked length spectra of some pairs of proper and cocompact cubical actions of a non-virtually cyclic group on $\text{CAT}(0)$ cube complexes. The cubulations are required to be virtually co-special, have the same sets of convex-cocompact subgroups, and admit a contracting element. There are many groups for which these conditions are always fulfilled for any pair of cubulations, including non-elementary cubulable hyperbolic groups, many cubulable relatively hyperbolic groups, and many right-angled Artin and Coxeter groups. For these pairs of cubulations, we study the Manhattan curve associated to their combinatorial metrics. We prove that this curve is analytic and convex, and a straight line if and only if the marked length spectra are homothetic. The same result holds if we consider invariant combinatorial metrics in which the lengths of the edges are not necessarily one. In addition, for their standard combinatorial metrics, we prove a large deviation theorem with shrinking intervals for their marked length spectra. We deduce the same result for pairs of word metrics on hyperbolic groups. The main tool is the construction of a finite-state automaton that simultaneously encodes the marked length spectra of both cubulations in a coherent way, in analogy with results about (bi)combable functions on hyperbolic groups by Calegari and Fujiwara. The existence of this automaton allows us to apply the machinery of thermodynamic formalism for suspension flows over subshifts of finite type, from which we deduce our results.