## Topology & Geometric Group Theory Seminar

## Fall 2008

### 1:30 – 2:30, Malott 406

Thursday, November 20

**Angela
Kubena Barnhill**, Northwestern University

*Density of commensurators of uniform lattices in right-angled
buildings*

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.

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