arXiv subjects
Publications and source records attributed to Valery V. Ryzhikov.
This note is devoted to infinite self-similar rank 1 constructions and their applications to the spectral theory of dynamical systems. The properties of orthogonal operators induced by self-similar constructions provide some unusual spectral properties of Gaussian and Poisson suspensions.
Answering the question of V.I. Oseledets, we present a random variable $ξ$ such that the sum $ξ(x)+aξ(y)$ has a singular distribution for a set of parameters $a$ dense in $(1, +\infty)$, but for another dense set of parameters, this sum has an absolutely continuous distribution. We prove the following assertion: given $C,D$, countable non-intersecting dense subsets of the ray $(1,+\infty)$, there is a measure-preserving flow $T_t$ (acting on the infinite Lebesgue space) such that automorphisms $T_1\otimes T_{c}$ have simple singular spectra for every $c\in C$, and $T_1\otimes T_{d}$ have Lebesgue spectra for all $d\in D$. The spectral measure of this flow plays the role of the distribution of our random variable $ξ$.
For any infinite zero-density integer set M, we found a rigid measure-preserving transformation mixing along M by answering Bergelson's question. Gaussian and Poisson suspensions over infinite constructions are suggested as suitable examples. We also discuss rigid rank one transformations of finite measure that mix along a given set, and some analogues for group actions.
This text is addressed to students. It is a short story about some problems in ergodic theory, both related and independent. We discuss the factorization of transformations into the product of three involutions; Furstenberg's theorem on weak multiple mixing in the mean along progressions; ergodic Furstenberg-Roth's theorem. In connection with Ledrappier's $Z^2$-action, we consider harmonic $Z_2$-sequences on $Z^2$ and experimentally observe the dominant infinite threads arising in them. The property of multiple mixing for systems with the Gordin ergodic group is proven. We discuss the absence of the Lehrer and Weiss property for the action of $\mathbb{Z}^2$-lattices, and Bergelson's question on sequence mixing. Some new open problems, unusual spectrum of a measure-preserving construction with related Katok's paradoxical effect are mentioned.
This text is written based on the author's publications during the period from 1991 to 2001. The work is devoted to the theory of Markov intertwining operators and joinings of measure-preserving group actions, as well as to their applications to study asymptotic properties of dynamical systems. Special attention is paid to Rokhlin's problems on multiple mixing and multiple spectrum. The development of these topics over the past twenty years has not been discussed. In fact many results on joinings have frozen in time, many questions have remained open without losing their relevance, but probably have ceased to excite interest due to difficulties. For example, it is not known whether the minimal self-joinings of order 2 imply all orders? Is there a non-trivial pairwise independent joining for a weakly mixing system of zero entropy? What can be said about such joinings for transformations with small local rank? These questions are ripe for a long time, and the author reminds the reader about them, combining his story with numerous partial and related results.
For a compact set of actions, an invariant of Kushnirenko's entropy type is chosen in such a way that on this set it is equal to zero, but will be infinity for typical actions. As a consequence, we show that typical measure-preserving transformations are not isomorphic to geometric shape exchange transformations. This problem arose in connection with the result of Chaika and Davis about the atypical nature of IETs.
The following question due to Thouvenot is well-known in ergodic theory. Let $S$ and $T$ be automorphisms of a probability space and let $ S \otimes S $ be isomorphic to $T \otimes T $. Could $S$ be not isomorphic to $T$? Our note contains a simple answer to this question and a generalization of Kulaga's result on the corresponding isomorphism for some class of flows (see arXiv:1101.4975). We show that the isomorphism of weakly mixing flows $ S_t \otimes S_t $ and $ T_t \otimes T_t $ implies the isomorphism of the flows $S_t$ and $T_t$, if the latter has an integral weak limit.
We consider a family of homoclinic groups and Gordin's type invariants of measure-preserving actions, state their connections with factors, full groups, ranks, rigidity, multiple mixing and realize such invariants in the class of Gaussian and Poisson suspensions.
Given an ergodic flow $T=(T_t)_{t\in\Bbb R}$, let $I(T)$ be the set of reals $s\ne 0$ for which the flows $(T_{st})_{t\in\Bbb R}$ and $T$ are isomorphic. It is proved that $I(T)$ is a Borel subset of $\Bbb R^*$. It carries a natural Polish group topology which is stronger than the topology induced from $\Bbb R$. There exists a mixing flow $T$ such that $I(T)$ is an uncountable meager subset of $\Bbb R^*$. For a generic flow $T$, the transformations $T_{t_1}$ and $T_{t_2}$ are spectrally disjoint whenever $|t_1|\ne |t_2|$. A generic transformation (i) embeds into a flow $T$ with $I(T)=\{1\}$ and (ii) does not embed into a flow with $I(T)\ne \{1\}$. For each countable multiplicative subgroup $S\subset\Bbb R^*$, it is constructed a Poisson suspension flow $T$ with simple spectrum such that $I(T)=S$. If $S$ is without rational relations then there is a rank-one weakly mixing rigid flow $T$ with $I(T)=S$.
Each subset $E\subset\Bbb N$ is realized as the set of essential values of the multiplicity function for the Koopman operator of an ergodic conservative infinite measure preserving transformation.
We introduce high staircase infinite measure preserving transformations and prove that they are mixing under a restricted growth condition. This is used to (i) realize each subset $E\subset\Bbb N\cup\{\infty\}$ as the set of essential values of the multiplicity function for the Koopman operator of a mixing ergodic infinite measure preserving transformation, (ii) construct mixing power weakly mixing infinite measure preserving transformations, (iii) construct mixing Poissonian automorphisms with a simple spectrum, etc.