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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
Supplementary Materials