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Rank-one non-singular actions of countable groups and their odometer factors

Published online by Cambridge University Press:  30 September 2024

ALEXANDRE I. DANILENKO*
Affiliation:
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Nauky Ave., Kharkiv 61164, Ukraine e-mail: alexandre.danilenko@gmail.com Mathematical Institute of the Polish Academy of Sciences, ul. Śniadeckich 8, Warszawa 00-656, Poland
MYKYTA I. VIEPRIK
Affiliation:
Mathematical Institute of the Polish Academy of Sciences, ul. Śniadeckich 8, Warszawa 00-656, Poland V. N. Karazin Kharkiv National University, 4 Svobody sq., Kharkiv 61077, Ukraine (e-mail: nikita.veprik@gmail.com)

Abstract

For an arbitrary countable discrete infinite group G, non-singular rank-one actions are introduced. It is shown that the class of non-singular rank-one actions coincides with the class of non-singular $(C,F)$-actions. Given a decreasing sequence of cofinite subgroups in G with $\bigcap _{n=1}^\infty \bigcap _{g\in G}g\Gamma _ng^{-1}=\{1_G\}$, the projective limit of the homogeneous G-spaces $G/\Gamma _n$ as $n\to \infty $ is a G-space. Endowing this G-space with an ergodic non-singular non-atomic measure, we obtain a dynamical system which is called a non-singular odometer. Necessary and sufficient conditions are found for a rank-one non-singular G-action to have a finite factor and a non-singular odometer factor in terms of the underlying $(C,F)$-parameters. Similar conditions are also found for a rank-one non-singular G-action to be isomorphic to an odometer. Minimal Radon uniquely ergodic locally compact Cantor models are constructed for the non-singular rank-one extensions of odometers. Several concrete examples are constructed and several facts are proved that illustrate a sharp difference of the non-singular non-commutative case from the classical finite measure preserving one: odometer actions which are not of rank-one and factors of rank-one systems which are not of rank one; however, each probability preserving odometer is a factor of an infinite measure preserving rank-one system, etc.

Type
Original Article
Copyright
© The Author(s), 2024. Published by Cambridge University Press

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