Cubulating surface‐by‐free groups

Abstract Let be an exact sequence where is the fundamental group of a closed surface of genus greater than one, is hyperbolic, and is finitely generated free. The aim of this paper is to provide sufficient conditions to prove that is cubulable and construct examples satisfying these conditions. The main result may be thought of as a combination theorem for virtually special hyperbolic groups when the amalgamating subgroup is not quasiconvex. Ingredients include the theory of tracks, the quasiconvex hierarchy theorem of Wise, the distance estimates in the mapping class group from subsurface projections due to Masur–Minsky, and the model geometry for doubly degenerate Kleinian surface groups used in the proof of the ending lamination theorem. An appendix to this paper by Manning, Mj, and Sageev proves a reduction theorem by showing that cubulability of follows from the existence of an essential incompressible quasiconvex track in a surface bundle over a graph with fundamental g\roup .