Pseudo-Anosovs from the perspective of their mapping tori

Abstract

In this chapter, we outline some of the many combinatorial tools developed over the past three decades for studying a pseudo-Anosov diffeomorphism of a surface by analyzing the geometry of its mapping torus. We begin with an overview of the various simplicial complexes associated with a surface (such as the curve, arc, and pants complexes) and explain how to relate the dynamics of the action of a given pseudo-Anosov on any one of these complexes to the dynamics of the diffeomorphism itself, or to the hyperbolic geometry of its mapping torus. We next cover some of the more modern features of the theory by discussing various analogs of pseudo-Anosov diffeomorphisms on surfaces of infinite type. We conclude with a description of original work-- due jointly to the author with Dave Futer and Sam Taylor-- that relates the action of a pseudo-Anosov on the curve complex to the minimum number of fixed points for any map in the corresponding isotopy class. The paper is written in as accessible a way as possible while assuming only the bare minimum in background. The hope is to informally convey to the reader some of the main ideas and strategies in the area.