A Birman-Hilden theorem for free groups

Geometry Topology Seminar
Monday, September 21, 2015 - 14:05
1 hour (actually 50 minutes)
Skiles 006
Rice University
The Birman-Hilden theorem relates the mapping class groups of two orientable surfaces S and X, given a regular branched covering map p from S to X. Explicitly, it provides an isomorphism between the group of mapping classes of S that have p-equivariant representatives (mod the deck group of the covering map), and the group of mapping classes of X that have representatives that lift to homeomorphisms of S. We will translate these notions into the realm of automorphisms of free group, and prove that an obvious analogue of the Birman-Hilden theorem holds there. To indicate the proof of this, we shall explore in detail several key examples, and we shall describe some group-theoretic applications of the theorem.  This is joint work with Rebecca Winarski, John Calabrese, and Tyrone Ghaswala