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Rigidity for group actions on homogeneous spaces by affine transformations
Published online by Cambridge University Press: 22 March 2016
Abstract
We give a criterion for the rigidity of the action of a group of affine transformations of a homogeneous space of a real Lie group. Let
$G$
be a real Lie group,
$\unicode[STIX]{x1D6EC}$
a lattice in
$G$
, and
$\unicode[STIX]{x1D6E4}$
a subgroup of the affine group
$\text{Aff}(G)$
stabilizing
$\unicode[STIX]{x1D6EC}$
. Then the action of
$\unicode[STIX]{x1D6E4}$
on
$G/\unicode[STIX]{x1D6EC}$
has the rigidity property in the sense of Popa [On a class of type
$\text{II}_{1}$
factors with Betti numbers invariants. Ann. of Math. (2)
163(3) (2006), 809–899] if and only if the induced action of
$\unicode[STIX]{x1D6E4}$
on
$\mathbb{P}(\mathfrak{g})$
admits no
$\unicode[STIX]{x1D6E4}$
-invariant probability measure, where
$\mathfrak{g}$
is the Lie algebra of
$G$
. This generalizes results of Burger [Kazhdan constants for
$\text{SL}(3,\mathbf{Z})$
. J. Reine Angew. Math.
413 (1991), 36–67] and Ioana and Shalom [Rigidity for equivalence relations on homogeneous spaces. Groups Geom. Dyn.
7(2) (2013), 403–417]. As an application, we establish rigidity for the action of a class of groups acting by automorphisms on nilmanifolds associated to two-step nilpotent Lie groups.
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- © Cambridge University Press, 2016