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Funktsional. Anal. i Prilozhen., 2024 Volume 58, Issue 2, Pages 115–136 (Mi faa4179)

On the conjugacy of measurable partitions with respect to the normalizer of a full type $\mathrm{II}_1$ ergodic group

Andrei Lodkina, Benzion Rubshteinb

a St. Petersburg State University, Mathematics and Mechanics Faculty
b Ben-Gurion University of the Negev, Israel

Abstract: Let $G$ be a countable ergodic group of automorphisms of a measure space $(X,\mu)$ and $\mathcal{N}[G]$ be the normalizer of its full group $[G]$. Problem: for a pair of measurable partitions $\xi$ and $\eta$ of the space $X$, when does there exist an element $g\in\mathcal{N}[G]$ such that $g\xi=\eta$? For a wide class of measurable partitions, we give a solution to this problem in the case where $G$ is an approximately finite group with finite invariant measure. As a consequence, we obtain results concerning the conjugacy of the commutative subalgebras that correspond to $\xi$ and $\eta$ in the type $\mathrm{II}_1$ factor constructed via the orbit partition of the group $G$.

Keywords: automorphisms of measurable space, orbit partitions, measurable partition, full group, normalizer, von Neumann factor.

MSC: 28Dxx, 37A20, 46Lxx

Received: 23.11.2023
Revised: 10.02.2024
Accepted: 20.02.2024

DOI: 10.4213/faa4179


 English version:
Functional Analysis and Its Applications, 2024, 58:2, 195–211

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© Steklov Math. Inst. of RAS, 2024