11/20/2003
Lee Mosher
Rutgers University - Newark
Parageometric automorphisms of free groups (joint work with Michael Handel)
Abstract
Geometric automorphims of free groups are those which are represented by an automorphisms of a surface with one hole. Parageometric automorphisms are those which are not geometric but which are represented, in some nice manner, by an automorphism of a certain 2-complex. We study the dynamics of parageometric automorphisms, finding analogies and constrasts with geometric automorphisms. As an application, we prove that the exponential growth rate of a parageometric automorphism (which is irreducible with irreducible powers) is strictly greater than the exponential growth rate of its inverse.