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JOURNALS // Funktsional'nyi Analiz i ego Prilozheniya // Archive

Funktsional. Anal. i Prilozhen., 2025 Volume 59, Issue 2, Pages 146–148 (Mi faa4239)

Tensor factorizations of a unitary operator with simple Lebesgue spectrum

Valerii Ryzhikov

Lomonosov Moscow State University, Faculty of Mechanics and Mathematics, Moscow, Russia

Abstract: We show that for all $n,p>1$, there exists a unitary operator $U$ such that the tensor product $U\otimes U^p\otimes\dots\otimes U^{p^{n-1}}$ is a unitary operator with simple Lebesgue spectrum. Moreover, there exists an ergodic automorphism $T$ such that the spectrum of $T\odot T$ is simple, while the spectrum of $T\otimes T\otimes T$ is absolutely continuous.

Keywords: automorphisms of measure spaces, unitary operator, tensor product, simple and absolutely continuous spectra.

MSC: 37A25, 37A30

Received: 17.06.2024
Revised: 07.08.2024
Accepted: 12.08.2024

DOI: 10.4213/faa4239


 English version:
Functional Analysis and Its Applications, 2025, 59:2, 218–220


© Steklov Math. Inst. of RAS, 2025