Nonergodic actions, cocycles and superrigidity.
Fisher, David, Morris, Dave Witte, Whyte, Kevin (2004)
The New York Journal of Mathematics [electronic only]
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Fisher, David, Morris, Dave Witte, Whyte, Kevin (2004)
The New York Journal of Mathematics [electronic only]
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Robert J. Zimmer (1978)
Annales scientifiques de l'École Normale Supérieure
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Alexandre Danilenko, Toshihiro Hamachi (2000)
Colloquium Mathematicae
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The orbit equivalence of type ergodic equivalence relations is considered. We show that it is equivalent to the outer conjugacy problem for the natural trace-scaling action of a countable dense ℝ-subgroup by automorphisms of the Radon-Nikodym skew product extensions of these relations. A similar result holds for the weak equivalence of arbitrary type cocycles with values in Abelian groups.
Robert J. Zimmer (1981)
Compositio Mathematica
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Alexandre Danilenko, Mariusz Lemańczyk (1999)
Studia Mathematica
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We establish existence and uniqueness of a canonical form for isometric extensions of an ergodic non-singular transformation T. This is applied to describe the structure of commutors of the isometric extensions. Moreover, for a compact group G, we construct a G-valued T-cocycle α which generates the ergodic skew product extension and admits a prescribed subgroup in the centralizer of .
Hawkins, Jane, Silva Cesar, E. (1998)
The New York Journal of Mathematics [electronic only]
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Artur Siemaszko (1994)
Studia Mathematica
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Compact group extensions of 2-fold simple actions of locally compact second countable amenable groups are considered. It is shown what the elements of the centralizer of such a system look like. It is also proved that each factor of such a system is determined by a compact subgroup in the centralizer of a normal factor.
Alexandre Danilenko (2000)
Colloquium Mathematicae
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We discuss the classification up to orbit equivalence of inclusions 𝑆 ⊂ ℛ of measured ergodic discrete hyperfinite equivalence relations. In the case of type III relations, the orbit equivalence classes of such inclusions of finite index are completely classified in terms of triplets consisting of a transitive permutation group G on a finite set (whose cardinality is the index of 𝑆 ⊂ ℛ), an ergodic nonsingular ℝ-flow V and a homomorphism of G to the centralizer of V.
Charles Pugh, Michael Shub (1971)
Compositio Mathematica
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