3/03/2011

Lee Mosher
Rutgers University

Nondistorted subgroups of Out(F_n), via Lipschitz retraction in spaces of trees (joint work with M. Handel)

We prove that various subgroups of Out(F_n) --- the outer automorphism group of a free group of rank n --- such as the stabilizer of the conjugacy class of a rank n-1 free factor, are undistorted in Out(F_n). The method of proof is to show that these subgroups are Lipschitz retracts of the ambient group, in fact we construct these retractions in appropriate spaces of trees on which F_n acts.