A note on the relation between Hartnell's firefighter problem and growth of groups

TL;DR

This paper explores the relationship between the firefighter problem's containment properties and the growth rates of groups, establishing equivalence for certain classes of groups using existing literature.

Contribution

It demonstrates that polynomial containment is equivalent to polynomial growth for elementary amenable and non-amenable groups, extending previous results.

Findings

Polynomial containment coincides with polynomial growth for elementary amenable groups.

Polynomial containment coincides with polynomial growth for non-amenable groups.

The equivalence does not hold in general for all graphs.

Abstract

The firefighter game problem on locally finite connected graphs was introduced by Bert Hartnell. The game on a graph $G$ can be described as follows: let $f_n$ be a sequence of positive integers; an initial fire starts at a finite set of vertices; at each (integer) time $n\geq 1$, $f_n$ vertices which are not on fire become protected, and then the fire spreads to all unprotected neighbors of vertices on fire; once a vertex is protected or is on fire, it remains so for all time intervals. The graph $G$ has the \emph{$f_n$-containment property} if every initial fire admits an strategy that protects $f_n$ vertices at time $n$ so that the set of vertices on fire is eventually constant. If the graph $G$ has the containment property for a sequence of the form $f_n=Cn^d$, then the graph is said to have \emph{polynomial containment}. In [5], it is shown that any locally finite graph with polynomial growth has polynomial containment; and it is remarked that the converse does not hold. That article also raised the question of whether the equivalence of polynomial growth and polynomial containment holds for Cayley graphs of finitely generated groups. In this short note, we remark how the equivalence holds for elementary amenable groups and for non-amenable groups from results in the literature.