Texas A&M University, Department of
Mathematics, 216 Milner Hall, 16th of April 2008, 3:00-3:50
Groups and Dynamics Seminar
Commensurators of uniform lattices in right-angled buildings
Angela Barnhill of Northwestern University
In the Lie group setting, Margulis proved that a lattice is arithmetic
if and only if its commensurator is dense. In the case of automorphism
groups of trees, Liu showed that every cocompact lattice has dense
commensurator. We consider commensurators of cocompact lattices in the
automorphism groups of right-angled buildings and show that the
commensurator of the "standard lattice" is dense. This is joint work
with Anne Thomas.