On Growth Functions of Coxeter Groups

Let $(W,S)$ be a Coxeter system of rank $n$ and let $p_{(W,S)}(t)$ be its growth function. It is known that $p_{(W,S)}(q^{-1})<\mathrm{\infty }$ holds for all $n\le q\in \mathbb{N}$. In this paper we will show that this still holds for $q=n-1$, if $(W,S)$ is $2$-spherical. Moreover, we will prove that $p_{(W,S)}(q^{-1})=\mathrm{\infty }$ holds for $q=n-2$, if the Coxeter diagram of $(W,S)$ is the complete graph. These two results provide a complete characterization of the finiteness of the growth function in the case of $2$-spherical Coxeter systems with complete Coxeter diagram.