Virtually free-by-cyclic groups

Abstract

We obtain a homological characterisation of virtually free-by-cyclic groups among groups that are hyperbolic and virtually compact special. As a consequence, we show that many groups known to be coherent actually possess the stronger property of being virtually free-by-cyclic. In particular, we show that all one-relator groups with torsion are virtually free-by-cyclic, solving a conjecture of Baumslag.

30 pages. Incorporated the referee's comments and corrections. Final version to appear in Geometric and Functional Analysis