Ergodic Theory and Dynamical Systems



Rigidity of weakly hyperbolic actions of higher real rank semisimple Lie groups and their lattices


GREGORY A. MARGULIS a1 and NANTIAN QIAN a1
a1 Department of Mathematics, Yale University, PO Box 208283, New Haven, CT 06520, USA (e-mail: {margulis,qian}@math.yale.edu)

Abstract

Under some weak hyperbolicity conditions, we establish C^0- and C^\infty-local rigidity theorems for two classes of standard algebraic actions: (1) left translation actions of higher real rank semisimple Lie groups and their lattices on quotients of Lie groups by uniform lattices; (2) higher rank lattice actions on nilmanifolds by affine diffeomorphisms. The proof relies on an observation that local rigidity of the standard actions is a consequence of the local rigidity of some constant cocycles. The C^0-local rigidity for weakly hyperbolic standard actions follows from a cocycle C^0-local rigidity result proved in the paper. The main ingredients in the proof of the latter are Zimmer's cocycle superrigidity theorem and stability properties of partially hyperbolic vector bundle maps. The C^\infty-local rigidity is deduced from the C^0-local rigidity following a procedure outlined by Katok and Spatzier.

Using similar considerations, we also establish C^0-global rigidity of volume preserving, higher rank lattice Anosov actions on nilmanifolds with a finite orbit.

(Received June 12 1999)
(Revised September 10 2000)