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On extension of cocycles to normalizer elements, outer conjugacy, and related problems
Authors:Alexandre I Danilenko  Valentin Ya Golodets
Institution:Department of Mechanics and Mathematics, Kharkov State University, Freedom Square 4, Kharkov, 310077, Ukraine ; Mathematics Department, Institute for Low Temperature Physics, Lenin Avenue 47, Kharkov, 310164, Ukraine
Abstract:Let $T$ be an ergodic automorphism of a Lebesgue space and $\alpha $ a cocycle of $T$ with values in an Abelian locally compact group $G$. An automorphism $\theta $ from the normalizer $NT]$ of the full group $T]$ is said to be compatible with $\alpha $ if there is a measurable function $\varphi : X \to G$ such that $\alpha (\theta x, \theta T\theta ^{-1}) = - \varphi (x) + \alpha (x, T) + \varphi (Tx)$ at a.e. $x$. The topology on the set $D(T, \alpha )$ of all automorphisms compatible with $\alpha $ is introduced in such a way that $D(T , \alpha )$ becomes a Polish group. A complete system of invariants for the $\alpha $-outer conjugacy (i.e. the conjugacy in the quotient group $D(T, \alpha )/T])$ is found. Structure of the cocycles compatible with every element of $NT]$ is described.

Keywords:Ergodic dynamical system  cocycle  outer conjugacy
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