Geodesics in the braid group on three strands

Abstract

We study the geodesic growth series of the braid group on three strands, B_3 := <a,b|aba = bab>. We show that the set of geodesics of B_3 with respect to the generating set S := {a,b,a^-1,b^-1} is a regular language, and we provide an explicit computation of the geodesic growth series with respect to this set of generators. In the process, we give a necessary and sufficient condition for a freely reduced word w in S^* to be geodesic in B_3 with respect to S. Also, we show that the translation length with respect to S of any element in B_3 is an integer.