Effective density of unipotent orbits
Presenter
May 14, 2015
Keywords:
- Raghunathan's theorem
- Ratner's theorem
- invariant measure
- periodic orbit
- horospherical subgroups
- dynamics on Lie groups
MSC:
- 37-xx
- 37Dxx
- 37D40
- 37Cxx
- 37C27
- 37C40
- 37C75
Abstract
Raghunathan conjectured that If G is a Lie group, Gamma a lattice, p in G/Gamma, and U an (ad-)unipotent group then the closure of U.p is homogeneous (a periodic orbit of a subgroup of G). This conjecture was proved by Ratner in the early 90's via the classification of invariant measures; significant special cases were proved earlier by Dani and Margulis using a different, topological dynamics approach. Neither of these proofs is effective, nor do they provide rates --- e.g. if p is generic in the sense that it does not lie on a
periodic orbit of any proper subgroup L