Lie Groups, Representations and Discrete Mathematics

Closed subgroups of the automorphism group of a tree which acts locally primitively have a rich structure theory. Combined with superrigidity for irreducible lattices in products of trees such that the projection in each factor is locally primitive one shows that such a lattice admits an infinite linear image over a field of charactersitic zero only when it is an extension of an arithmetic lattice. Joint work with Marc Burger and Bob Zimmer