Twisted conjugacy classes of Automorphisms of Baumslag-Solitar groups

Abstract

Let φ : G → G be a group endomorphism where G is a finitely generated group of exponential growth, and denote by R(φ) the number of twisted φ-conjugacy classes. Fel’shtyn and Hill [7] conjectured that if φ is injective, then R(φ) is infinite. This conjecture is true for automorphisms of non-elementary Gromov hyperbolic groups, see [17] and [6]. It was showed in [12] that the conjecture does not hold in general. Nevertheless in this paper, we show that the conjecture holds for injective homomorphisms for the family of the Baumslag-Solitar groups B(m,n) where m 6= n and either m or n is greater than 1, and for automorphisms for the case m = n > 1. family of the Baumslag-Solitar groups B(m,n) where m 6= n.