Infinite Groups Seminar: Willis, Piggott

The next Infinite Groups Seminar will be held at the University of Newcastle on Monday
14 February.  The schedule is below.  Please get in touch if you are interested in
getting the train to/from Newcastle with me - Anne.  

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The seminar will be held in Room V206 of the Mathematics building and the two talks will
be at 12:00 and 2:00.  

12:00 George Willis, University of Newcastle 

TITLE: Rigidity of Homomorphisms from Arithmetic Groups to Totally Disconnected Groups 

ABSTRACT: The talk will explain joint work with Yehuda Shalom showing that the only
homomorphisms from certain arithmetic groups to totally disconnected, locally compact
groups are the obvious, or naturally occurring, ones.  For these groups, this extends
the supperrigidity theorem that G.  Margulis proved for homomorphisms from high rank
arithmetic groups to Lie groups.  

The theorems will be illustrated by referring to the groups $SL_3(\mathbb{Z})$,
$SL_2(\mathbb{Z}[\sqrt{2}])$ and $SL_3(\mathbb{Q})$.  

2:00 Adam Piggott, Bucknell University 

TITLE: The automorphisms of McCullough-Miller space 

ABSTRACT: McCullough-Miller space X = X(W) is a topological model for the outer
automorphism group of a free product of groups W.  We will discuss the question of just
how good a model it is.  In particular, we consider circumstances under which Aut(X) is
precisely Out(W).