On Multiple Recurrence

On the multiple recurrence properties for disjoint systems

We consider mutually disjoint family of measure preserving transformations $T_1, \cdots, T_k$ on a probability space $(X, \mathcal{B}, μ)$. We obtain the multiple recurrence property of $T_1, \cdots, T_k$ and this result is utilized to derive multiple recurrence of Poincaré type in metric spaces. We also present multiple recurrence property of Khintchine type. Further, we study multiple ergodic averages of disjoint systems and we show that $T_1, \cdots, T_k$ are uniformly jointly ergodic if each $T_i$ is ergodic.

Multiple recurrence for two commuting transformations

This paper is devoted to a study of the multiple recurrence of two commuting transformations. We derive a result which is similar but not identical to that of one single transformation established by Bergelson, Host and Kra. We will use the machinery of "magic systems" established recently by B. Host for the proof.

An Application of Topological Multiple Recurrence to Tiling

We show that given any tiling of Euclidean space, any geometric patterns of points, we can find a patch of tiles (of arbitrarily large size) so that copies of this patch appear in the tiling nearly centered on a scaled and translated version of the pattern. The rather simple proof uses Furstenberg's topological multiple recurrence theorem.

Multiple recurrence and convergence results associated to $\mathbb{F}_{p}^ω$-actions

Using an ergodic inverse theorem obtained in our previous paper, we obtain limit formulae for multiple ergodic averages associated with the action of $\mathbb{F}_{p}^ω$. From this we deduce multiple Khintchine-type recurrence results analogous to those for $\mathbb{Z}$-systems obtained by Bergelson, Host, and Kra, and also present some new counterexamples in this setting.

Discrete multitime multiple recurrence

The aim of our paper is to formulate and solve problems concerning multitime multiple recurrence equations. We discuss in detail the generic properties and the existence and uniqueness of solutions. Among the general things, we discuss in detail the cases of autonomous and non-autonomous recurrences, highlighting in particular the theorems of existence and uniqueness of solutions. Finally, are given interesting examples which are the analogue of arithmetic progression and the analogue of geometric progression. The multitime multiple recurrences are required in analysis of algorithms, computati…

An extension of Furstenberg's structure theorem for Noetherian modules and multiple recurrence theorems II

Using a recent Furstenberg structure theorem, we obtain a quantitative multiple recurrence theorem relative to any locally compact second countable Noetherian module over a syndetic ring.

Intersection spaces and multiple transverse recurrence

We study multiple recurrence properties along separated cross sections for pmp actions of unimodular lcsc group on Polish spaces. We establish a multiple transverse recurrence theorem under the assumption that sufficiently large powers of the return time set are Delone sets. Typical examples of such situations arise from the theory of uniform approximate lattices.

Discrete linear multiple recurrence with multi-periodic coefficients

The aim of our paper is to formulate and solve problems concerning linear multiple periodic recurrence equations. Among other things, we discuss in detail the cases with periodic and multi-periodic coefficients, highlighting in particular the theorems of Floquet type. For this aim, we find specific forms for the fundamental matrix. Explicitly monodromy matrix is given, and its eigenvalues (called Floquet multipliers) are shown. The Floquet point of view brings about an important simplification: the initial linear multiple recurrence system is reduced to another linear multiple recurrence syste…

关于阿尔韦斯（Alweiss）的多重递归示例

On Alweiss's example for multiple recurrence

探讨R. Alweiss给出的示例，构造出与每个幂零 - 玻尔集相交却非2 - 递归集的自然数集S。

Linear discrete multitime multiple recurrence

The multitime multiple recurrences are common in analysis of algorithms, computational biology, information theory, queueing theory, filters theory, statistical physics etc. The theoretical part about them is little or not known. That is why, the aim of our paper is to formulate and solve problems concerning nonautonomous multitime multiple recurrence equations. Among other things, we discuss in detail the cases of linear recurrences with constant coefficients, highlighting in particular the theorems of existence and uniqueness of solutions.

Closest integer polynomial multiple recurrence along shifted primes

Following an approach presented by N. Frantzikinakis, B. Host and B. Kra, we show that the parameters in the multidimensional Szemerédi theorem for closest integer polynomials have non-empty intersection with the set of shifted primes $\mathbb{P}-1$ (or similarly of $\mathbb{P}+1$). Using the Furstenberg Correspondence Principle, we show this result by recasting it as a polynomial multiple recurrence result in measure ergodic theory. Furthermore, we obtain integer part polynomial convergence results by the same method, which is a transference principle that enables one to deduce results for $\…

关于无限和集与多重回复集

On infinite sumsets and sets of multiple recurrence

本文回答了关于稠密与稀疏整数集中无限和集存在性及其与回复集关系的两个问题，并推广结果，得到多重可测与拓扑回复集的新刻画。

A local limit theorem for number of multiple recurrences generated by some mixing processes with applications to Young towers

We prove a local central limit theorem for "nonconventional" sums generated by some classes of sufficiently fast mixing sequences.

An extension of Furstenberg's structure theorem for Noetherian modules and multiple recurrence theorems I

We extend Furstenberg's structure theorem to any standard Borel $G$-space, where $G$ is any locally compact second countable Noetherian module over a syndetic ring.

韦尔系统中的多项式递归

Multiple Polynomial Recurrence in Weyl Systems

本文研究了韦尔系统中的多项式递归问题，证明了可测递归与拓扑递归的一致性，并提出了韦尔多项式的新概念。

Multiple recurrence for non-commuting transformations along rationally independent polynomials

We prove a multiple recurrence result for arbitrary measure-preserving transformations along polynomials in two variables of the form $m+p_i(n)$, with rationally independent $p_i$'s with zero constant term. This is in contrast to the single variable case, in which even double recurrence fails unless the transformations generate a virtually nilpotent group. The proof involves reduction to nilfactors and an equidistribution result on nilmanifolds.

Polynomial multiple recurrence over rings of integers

We generalize the polynomial Szemerédi theorem to intersective polynomials over the ring of integers of an algebraic number field, by which we mean polynomials having a common root modulo every ideal. This leads to the existence of new polynomial configurations in positive-density subsets of $\mathbb{Z}^m$ and strengthens and extends recent results of Bergelson, Leibman and Lesigne on polynomials over the integers.

A good universal weight for multiple recurrence averages with commuting transformations in norm

We will show that the sequences appearing in Bourgain's double recurrence result are good universal weights to the multiple recurrence averages with commuting measure-preserving transformations in norm. This will extend the pointwise converge result of Bourgain, the norm convergence result of Tao, and the authors' previous work on the single measure-preserving transformation.

Multiple recurrence and convergence for certain averages along shifted primes

We show any subset $A\subset\mathbb{N}$ with positive upper Banach density contains the pattern $\{m,m+[nα],\dots,m+k[nα]\}$, for some $m\in\mathbb{N}$ and $n=p-1$ for some prime $p$, where $α\in\mathbb{R}\backslash\mathbb{Q}$. Making use for the Furstenberg Correspondence Principle, we do this by proving an associated recurrence result in ergodic theory along the shifted primes. We also prove the convergence result for the associated averages along primes and indicate other applications of these methods.

Multiple Recurrence and Algorithmic Randomness

This work contributes to the programme of studying effective versions of "almost everywhere" theorems in analysis and ergodic theory via algorithmic randomness. We determine the level of randomness needed for a point in a Cantor space $ \{0,1\}^{\NN}$ with the uniform measure and the usual shift so that effective versions of the multiple recurrence theorem of Furstenberg holds for iterations starting at the point. We consider recurrence into closed sets that possess various degrees of effectiveness: clopen, $\PPI$ with computable measure, and $\PPI$. The notions of Kurtz, Schnorr, and \ML\ ran…

Topological multiple recurrence of weakly mixing minimal systems for generalized polynomials

Let $(X, T)$ be a weakly mixing minimal system, $p_1, \cdots, p_d$ be integer-valued generalized polynomials and $(p_1,p_2,\cdots,p_d)$ be non-degenerate. Then there exists a residual subset $X_0$ of $X$ such that for all $x\in X_0$ $$\{ (T^{p_1(n)}x, \cdots, T^{p_d(n)}x): n\in \mathbb{Z}\}$$ is dense in $X^d$.

Recurrence for stationary group actions

Using a structure theorem from [FG2010] we prove a version of multiple recurrence for sets of positive measure in a general stationary dynamical system.

Multiple recurrence and convergence without commutativity

We establish multiple recurrence and convergence results for pairs of zero entropy measure preserving transformations that do not satisfy any commutativity assumptions. Our results cover the case where the iterates of the two transformations are $n$ and $n^k$ respectively, where $k\geq 2$, and the case $k=1$ remains an open problem. Our starting point is based on the observation that Furstenberg systems of sequences of the form $(f(T^{n^k}x))$ have very special structural properties when $k\geq 2$. We use these properties and some disjointness arguments in order to get characteristic factors w…

Host-Kra theory for $\bigoplus_{p\in P}\mathbb{F}_p$- Systems and multiple recurrence

Let $\mathcal{P}$ be an (unbounded) countable multiset of primes (i.e. every prime may appear multiple times) and let $G=\bigoplus_{p\in \mathcal{P}}\mathbb{F}_p$. We develop a Host-Kra structure theory for the universal characteristic factors of an ergodic $G$-system. More specifically, we generalize the main results of Bergelson Tao and Ziegler who studied these factors in the special case $\mathcal{P}=\{p,p,p,...\}$ for some fixed prime $p$. As an application we deduce a Khintchine-type recurrence theorem in the flavor of Bergelson Tao and Ziegler and Bergelson Host and Kra.

A view on multiple recurrence

In this note we present a proof of multiple recurrence for ergodic systems (and thereby of Szemerédi's theorem) being a mixture of three known proofs. It is based on a conditional version of the Jacobs-de Leeuw-Glicksberg decomposition and properties of the Gowers-Host-Kra uniformity seminorms.

A nilpotent IP polynomial multiple recurrence theorem

We generalize the IP-polynomial Szemerédi theorem due to Bergelson and McCutcheon and the nilpotent Szemerédi theorem due to Leibman. Important tools in our proof include a generalization of Leibman's result that polynomial mappings into a nilpotent group form a group and a multiparameter version of the nilpotent Hales-Jewett theorem due to Bergelson and Leibman.

On Multiple and Polynomial Recurrent extensions of infinite measure preserving transformations

We prove that multiple-recurrence and polynomial-recurrence of invertible infinite measure preserving transformations are both properties which pass to extensions.

Single and multiple recurrence along non-polynomial sequences

We establish new recurrence and multiple recurrence results for a rather large family $\mathcal{F}$ of non-polynomial functions which includes tempered functions defined in [11], as well as functions from a Hardy field with the property that for some $\ell\in \mathbb{N}\cup\{0\}$, $\lim_{x\to\infty }f^{(\ell)}(x)=\pm\infty$ and $\lim_{x\to\infty }f^{(\ell+1)}(x)=0$. Among other things, we show that for any $f\in\mathcal{F}$, any invertible probability measure preserving system $(X,\mathcal{B},μ,T)$, any $A\in\mathcal{B}$ with $μ(A)>0$, and any $ε>0$, the sets of returns $$ R_{ε, A}= \big\{n\in…

van der Corput差分定理的推广及其在回复性与多重遍历平均中的应用

A generalization of van der Corput's difference theorem with applications to recurrence and multiple ergodic averages

本文将van der Corput差分定理推广到Hilbert空间向量序列，借助新Hilbert空间中谱型绝对连续的条件，并应用于非交换保测自同构下的回复性与多重遍历平均问题。

非极大环面作用的刚性、幂单定量回复与丢番图逼近

Rigidity of non-maximal torus actions, unipotent quantitative recurrence, and Diophantine approximations

本文通过沿幂单方向的定量回复方法，给出了高阶对角化作用在 $SL_2$ 形式算术商上正熵测度的分类及其 Adelic 版本，并应用于整数倍丢番图逼近问题。

无交换性条件下的多重回复

Multiple recurrence without commutativity

该研究针对无交换性的多重回复问题，证明两个极小同胚映射系统中存在剩余子集，对其上任意点与零值非线性整系数多项式，存在整数子列使映射迭代均收敛到该点。

Multiple recurrence and the structure of probability-preserving systems

In 1975 Szemerédi proved the long-standing conjecture of Erdős and Turán that any subset of $\bbZ$ having positive upper Banach density contains arbitrarily long arithmetic progressions. Szemerédi's proof was entirely combinatorial, but two years later Furstenberg gave a quite different proof of Szemerédi's Theorem by first showing its equivalence to an ergodic-theoretic assertion of multiple recurrence, and then bringing new machinery in ergodic theory to bear on proving that. His ergodic-theoretic approach subsequently yielded several other results in extremal combinatorics, as well as revea…

Ergodic-theoretic implementations of the Roth density-increment argument

We exhibit proofs of two ergodic-theoretic results in the study of multiple recurrence using an analog of the density-increment argument of Roth and Gowers: Furstenberg's Multiple Recurrence Theorem (which implies Szemerédi's Theorem), and a two-dimensional special case of Furstenberg and Katznelson's multidimensional version of this theorem. The second of these requires also an analog of some recent finitary work by Shkredov. Many proofs of these multiple recurrence theorems are now known, but our main goal is to shed some further light on the heuristic correspondence principle that has grown…

Powers of sequences and recurrence

We study recurrence, and multiple recurrence, properties along the $k$-th powers of a given set of integers. We show that the property of recurrence for some given values of $k$ does not give any constraint on the recurrence for the other powers. This is motivated by similar results in number theory concerning additive basis of natural numbers. Moreover, motivated by a result of Kamae and Mendès-France, that links single recurrence with uniform distribution properties of sequences, we look for an analogous result dealing with higher order recurrence and make a related conjecture.

Quantitative multiple recurrence for two and three transformations

We provide various counter examples for quantitative multiple recurrence problems for systems with more than one transformation. We show that $\bullet$ There exists an ergodic system $(X,\mathcal{X},μ,T_1,T_2)$ with two commuting transformations such that for every $0<\ell< 4$, there exists $A\in\mathcal{X}$ such that $$μ(A\cap T_{1}^{-n}A\cap T_{2}^{-n}A)<μ(A)^{\ell} \text{ for every } n\neq 0;$$ $\bullet$ There exists an ergodic system $(X,\mathcal{X},μ,T_1,T_2, T_{3})$ with three commuting transformations such that for every $\ell>0$, there exists $A\in\mathcal{X}$ such that $$μ(A\cap T_{1}…

Multiple recurrence in quasirandom groups

We establish a new mixing theorem for quasirandom groups (finite groups with no low-dimensional unitary representations) $G$ which, informally speaking, asserts that if $g, x$ are drawn uniformly at random from $G$, then the quadruple $(g,x,gx,xg)$ behaves like a random tuple in $G^4$, subject to the obvious constraint that $gx$ and $xg$ are conjugate to each other. The proof is non-elementary, proceeding by first using an ultraproduct construction to replace the finitary claim on quasirandom groups with an infinitary analogue concerning a limiting group object that we call an \emph{ultra quas…

Szemeredi's theorem, frequent hypercyclicity and multiple recurrence

Let T be a bounded linear operator acting on a complex Banach space X and (λ_n) a sequence of complex numbers. Our main result is that if |λ_n|/|λ_{n+1}| \to 1 and the sequence (λ_n T^n) is frequently universal then T is topologically multiply recurrent. To achieve such a result one has to carefully apply Szemerédi's theorem in arithmetic progressions. We show that the previous assumption on the sequence (λ_n) is optimal among sequences such that |λ_n|/|λ_{n+1}| converges in [0,+\infty]. In the case of bilateral weighted shifts and adjoints of multiplication operators we provide characterizati…

Multiple ergodic averages in abelian groups and Khintchine type recurrence

Let $G$ be a countable abelian group. We study ergodic averages associated with configurations of the form $\{ag,bg,(a+b)g\}$ for some $a,b\in\mathbb{Z}$. Under some assumptions on $G$, we prove that the universal characteristic factor for these averages is a factor of a $2$-step nilpotent homogeneous space. As an application we derive a Khintchine type recurrence result. In particular, we prove that for every countable abelian group $G$, if $a,b\in\mathbb{Z}$ are such that $aG,bG,(b-a)G$ and $(a+b)G$ are of finite index in $G$, then for every $E\subset G$ and $\varepsilon>0$ the set $$\{g\in …

高阶Wiener-Wintner系统：示例与应用

Higher Order Wiener-Wintner systems: examples and applications

本研究构建高维Wiener-Wintner动力系统，通过扩展Bourgain的双重回归估计实现多重遍历平均的定量控制，给出多重回归相关平均几乎处处收敛的简洁证明，并提供Host-Kra-Ziegler因子的新特征。

沿广义勾股数的矫饰系统的递归性

Recurrence for pretentious systems along generalized Pythagorean triples

针对沿广义勾股数（方程$ax^2 + b y^2 = c z^2$的解）的矫饰保测乘法作用建立多重递归结果，证实广义勾股分划正则性猜想的遍历理论形式，推论得相关有限着色自然数集含单色广义勾股数。

Rationally almost periodic sequences, polynomial multiple recurrence and symbolic dynamics

A set $R\subset \mathbb{N}$ is called rational if it is well-approximable by finite unions of arithmetic progressions. Examples of rational sets include many classical sets of number-theoretical origin such as the set of squarefree numbers, the set of abundant numbers, or sets of the form $Φ_x:=\{n\in\mathbb{N}: \frac{\boldsymbolφ(n)}{n}<x\}$, where $x\in[0,1]$ and $\boldsymbolφ$ is Euler's totient function. We investigate the combinatorial and dynamical properties of rational sets and obtain new results in ergodic Ramsey theory. We show that if $R$ is a rational set with $\overline{d}(R)>0$, …

可计算保测变换的有效回归性

Effective recurrence for computable measure-preserving transformations

本文研究了可计算保测变换下庞加莱回归的有效条件，提出了$\Pi^0_n$-生成性等新概念，并给出了正频率回归的充分必要条件。

加权平均及其在多重回复集中的应用

Weighted averages and applications to sets of multiple recurrence

本文通过引入快速增长权重的加权平均技术，推广了Szemerédi定理，证实了Bergelson-Moreira-Richter猜想，并涵盖了多项式Szemerédi定理及平滑函数下的多重回复厚集结果，同时推广了Boshernitzan均匀分布准则。

Multiple recurrence and large intersections for abelian group actions

The purpose of this paper is to study the phenomenon of large intersections in the framework of multiple recurrence for measure-preserving actions of countable abelian groups. Among other things, we show: (1) If $G$ is a countable abelian group and $φ, ψ: G \to G$ are homomorphisms such that $φ(G)$, $ψ(G)$, and $(ψ- φ)(G)$ have finite index in $G$, then for every ergodic measure-preserving system $(X, \mathcal{B}, μ, (T_g)_{g \in G})$, every set $A \in \mathcal{B}$, and every $\varepsilon > 0$, the set $\{g \in G : μ(A \cap T_{φ(g)}^{-1}A \cap T_{ψ(g)}^{-1}A) > μ(A)^3 - \varepsilon\}$ is synde…

Nonconventional ergodic averages and multiple recurrence for von Neumann dynamical systems

The Furstenberg recurrence theorem (or equivalently, Szemerédi's theorem) can be formulated in the language of von Neumann algebras as follows: given an integer $k \geq 2$, an abelian finite von Neumann algebra $(\M,τ)$ with an automorphism $α: \M \to \M$, and a non-negative $a \in \M$ with $τ(a)>0$, one has $\liminf_{N \to \infty} \frac{1}{N} \sum_{n=1}^N \Re τ(a α^n (a) ... α^{(k-1)n} (a)) > 0$; a subsequent result of Host and Kra shows that this limit exists. In particular, $\Re τ(a α^n (a) >... α^{(k-1)n} (a)) > 0$ for all $n$ in a set of positive density. From the von Neumann algebra pers…

Optimal lower bounds for multiple recurrence

Let $(X, \mathcal{B},μ,T)$ be an ergodic measure preserving system, $A \in \mathcal{B}$ and $ε>0$. We study the largeness of sets of the form \begin{equation*} \begin{split} S = \left\{ n\in\mathbb{N}\colonμ(A\cap T^{-f_1(n)}A\cap T^{-f_2(n)}A\cap\ldots\cap T^{-f_k(n)}A)> μ(A)^{k+1} - ε\right\} \end{split} \end{equation*} for various families $\{f_1,\dots,f_k\}$ of sequences $f_i\colon \mathbb{N} \to \mathbb{N}$. For $k \leq 3$ and $f_{i}(n)=i f(n)$, we show that $S$ has positive density if $f(n)=q(p_n)$ where $q \in \mathbb{Z}[x]$ satisfies $q(1)$ or $q(-1) =0$ and $p_n$ denotes the $n$-th pr…

Multiple recurrence and convergence for Hardy sequences of polynomial growth

We study the limiting behavior of multiple ergodic averages involving sequences of integers that satisfy some regularity conditions and have polynomial growth. We show that for "typical" choices of Hardy field functions $a(t)$ with polynomial growth, the averages $\frac{1}{N}\sum_{n=1}^N f_1(T^{[a(n)]}x)\cdot...\cdot f_\ell(T^{\ell [a(n)]}x)$ converge in the mean and we determine their limit. For example, this is the case if $a(t)=t^{3/2}, t\log{t},$ or $t^2+(\log{t})^2$. Furthermore, if ${a_1(t),...,a_\ell(t)}$ is a "typical" family of logarithmico-exponential functions of polynomial growth, …

Rigidity, weak mixing, and recurrence in abelian groups

The focus of this paper is the phenomenon of rigidity for measure-preserving actions of countable discrete abelian groups and its interactions with weak mixing and recurrence. We prove that results about $\mathbb{Z}$-actions extend to this setting: 1. If $(a_n)$ is a rigidity sequence for an ergodic measure-preserving system, then it is a rigidity sequence for some weakly mixing system. 2. There exists a sequence $(r_n)$ such that every translate is both a rigidity sequence and a set of recurrence. The first of these results was shown for $\mathbb{Z}$-actions by Adams, Fayad and Thouvenot, and…