Ergodic Theory: Recurrence

拉格朗日庞加莱回归的一个反例

A counterexample to Lagrangian Poincaré recurrence

该研究构造了反例，证伪了6维及更高维情形下Ginzburg和Viterbo提出的拉格朗日庞加莱回归猜想。

遍历流的积分零点回归

Recurrence of integral zeros for ergodic flows

本文证明了保遍历概率测度的流上积分零点的回归性质：在正测度集上几乎处处存在时间序列，使轨道回归该集且积分值为零。

Infinite-horizon Lorentz tubes and gases: recurrence and ergodic properties

We construct classes of two-dimensional aperiodic Lorentz systems that have infinite horizon and are 'chaotic', in the sense that they are (Poincaré) recurrent, uniformly hyperbolic, ergodic, and the first-return map to any scatterer is $K$-mixing. In the case of the Lorentz tubes (i.e., Lorentz gases in a strip), we define general measured families of systems (\emph{ensembles}) for which the above properties occur with probability 1. In the case of the Lorentz gases in the plane, we define families, endowed with a natural metric, within which the set of all chaotic dynamical systems is uncoun…

Recurrence and higher ergodic properties for quenched random Lorentz tubes in dimension bigger than two

We consider the billiard dynamics in a non-compact set of R^d that is constructed as a bi-infinite chain of translated copies of the same d-dimensional polytope. A random configuration of semi-dispersing scatterers is placed in each copy. The ensemble of dynamical systems thus defined, one for each global realization of the scatterers, is called `quenched random Lorentz tube'. Under some fairly general conditions, we prove that every system in the ensemble is hyperbolic and almost every system is recurrent, ergodic, and enjoys some higher chaotic properties.

超越庞加莱回归：关于曲面上流的轨道拓扑三分法及极限集依赖性的研究

Beyond Poincar{é} recurrence: on a topological trichotomy of orbits and on the dependence of limit sets for flows on surfaces

本文提出曲面上连续流轨道的拓扑三分法，引入游荡全纯回路和严格极限回路概念，揭示非回归行为与极限集依赖性的关系，并给出极小流的充要条件。

四维空间中Lagrangian庞加莱复发的反例

A counterexample to Lagrangian Poincaré recurrence in dimension four

本文通过近托里纤维化在四维空间中构造了Lagrangian庞加莱复发的反例，挑战了传统理论。

四维中拉格朗日庞加莱回归的更多反例

More counterexamples to Lagrangian Poincaré recurrence in dimension four

本文扩展了拉格朗日庞加莱回归的反例族，使其覆盖所有非单调环面辛四流形，补充了作者早前关于环面辛四流形反例的研究。

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.

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。

遍历变换讲义

Lecture notes on ergodic transformations

本讲义系统介绍了遍历变换的核心理论，涵盖遍历性等价性质、Birkhoff定理、弱混合、典型熵不变量、Poisson悬浮及酉算子谱定理等关键主题。

Approximate Identities and Lagrangian Poincaré Recurrence

In this note we discuss three interconnected problems about dynamics of Hamiltonian or, more generally, just smooth diffeomorphisms. The first two concern the existence and properties of the maps whose iterations approximate the identity map with respect to some norm, e.g., $C^1$- or $C^0$-norm for general diffeomorphisms and the $γ$-norm in the Hamiltonian case, and the third problem is the Lagrangian Poincaré recurrence conjecture.

The Poincaré Recurrence Problem of Inviscid Incompressible Fluids

Nadirashvili presented a beautiful example showing that the Poincaré recurrence does not occur near a particular solution to the 2D Euler equation of inviscid incompressible fluids. Unfortunately, Nadirashvili's setup of the phase space is not appropriate, and details of the proof are missing. This note fixes that.

The Kac formula and Poincaré recurrence theorem in Riesz spaces

Riesz space (non-pointwise) generalizations for iterative processes are given for the concepts of recurrence, first recurrence and conditional ergodicity. Riesz space conditional versions of the Poincaré Recurrence Theorem and the Kac formula are developed. Under mild assumptions, it is shown that every conditional expectation preserving process is conditionally ergodic with respect to the conditional expectation generated by the Cesàro mean associated with the iterates of the process. Applied to processes in $L^1(Ω,{\mathcal A},μ)$, where $μ$ is a probability measure, new conditional versions…

庞加莱回归与收缩目标问题的极限定律

Limit Laws for Poincaré Recurrence and the Shrinking Target Problem

针对满足指数多重去相关和短返回条件的保测系统，建立了庞加莱回归的分布律，并验证了公理A系统的强不变原理。

$ω$-recurrence in cocycles

After relating the notion of $ω$-recurrence in skew products to the range of values taken by partial ergodic sums and Lyapunov exponents, ergodic $\mathbb{Z}$-valued cocycles over an irrational rotation are presented in detail. First, the generic situation is studied and shown to be $1/n$-recurrent. It is then shown that for any $ω(n) <n^{-ε}$, where $ε>1/2$, there are uncountably many infinite staircases (a certain specific cocycle over a rotation) which are \textit{not} $ω$-recurrent, and therefore have positive Lyapunov exponent. A further section makes brief remarks regarding cocycles over…

Potential well in Poincaré recurrence

From a physical/dynamical system perspective, the potential well represents the proportional mass of points that escape the neighbourhood of a given point. In the last 20 years, several works have shown the importance of this quantity to obtain precise approximations for several recurrence time distributions in mixing stochastic processes and dynamical systems. Besides providing a review of the different scaling factors used in the literature in recurrence times, the present work contributes with two new results: (1) for $ϕ$-mixing and $ψ$-mixing processes, we give a new exponential approximat…

论有效Banach-Mazur博弈及其在范畴Poincaré回归定理中的应用

On Effective Banach-Mazur Games and an application to the Poincaré Recurrence Theorem for Category

通过有效化Banach-Mazur博弈，刻画有效第一范畴集，并给出有效Banach范畴定理的证明，进而用博弈论方法证明动力系统中范畴Poincaré回归定理的有效版本。

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…

Ergodic recurrence and bounded gaps between primes

Let $(X,B_X,μ,T)$ be a measure-preserving probability system with $T$ is invertible. Suppose that $A\in B_X$ with $μ(A)>0$ and $ε>0$. For any $m\geq 1$, there exist infinitely many primes $p_0,p_1,\ldots,p_m$ with $p_0<\cdots<p_m$ such that $$ μ(A\cap T^{-(p_i-1)}A)\geq μ(A)^2-ε$$ for each $0\leq i\leq m$ and $$ p_m-p_0<C_m, $$ where $C_m>0$ is a constant only depending on $m$, $A$ and $ε$.

Extended orbit properties on surfaces

In this paper, we study "demi-caractéristique" and (Poisson) stability in the sense of Poincaré. Using the definitions á la Poincaré for $\R$-actions $v$ on compact connected surfaces, we show that "$R$-closed" $\Rightarrow$ "pointwise almost periodicity (p.a.p.)" $\Rightarrow$ "recurrence" $\Rightarrow$ non-wandering. Moreover, we show that the action $v$ is "recurrence" with $|\mathrm{Sing}(v)| < \infty$ iff $v$ is regular non-wandering. If there are no locally dense orbits, then $v$ is "p.a.p." iff $v$ is "recurrence" without "orbits" containing infinitely singularities. If $|\mathrm{Sing}(…

Lorenz like flows: exponential decay of correlations for the Poincaré map, logarithm law, quantitative recurrence

In this paper we prove that the Poincaré map associated to a Lorenz like flow has exponential decay of correlations with respect to Lipschitz observables. This implies that the hitting time associated to the flow satisfies a logarithm law. The hitting time $τ_r(x,x_0)$ is the time needed for the orbit of a point $x$ to enter for the first time in a ball $B_r(x_0)$ centered at $x_0$, with small radius $r$. As the radius of the ball decreases to 0 its asymptotic behavior is a power law whose exponent is related to the local dimension of the SRB measure at $x_0$: for each $x_0$ such that the loca…

What is the mechanism of power-law distributed Poincaré recurrences in higher-dimensional systems?

The statistics of Poincaré recurrence times in Hamiltonian systems typically shows a power-law decay with chaotic trajectories sticking to some phase-space regions for long times. For higher-dimensional systems the mechanism of this power-law trapping is still unknown. We investigate trapped orbits of a generic 4D symplectic map in phase space and frequency space and find that, in contrast to 2D maps, the trapping is (i) not due to a hierarchy in phase space. Instead, it occurs at the surface of the regular region, (ii) outside of the Arnold web. The chaotic dynamics in this sticky region is (…

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…

From Darwin to Poincaré and von Neumann: Recurrence and Cycles in Evolutionary and Algorithmic Game Theory

Replicator dynamics, the continuous-time analogue of Multiplicative Weights Updates, is the main dynamic in evolutionary game theory. In simple evolutionary zero-sum games, such as Rock-Paper-Scissors, replicator dynamic is periodic \cite{zeeman1980population}, however, its behavior in higher dimensions is not well understood. We provide a complete characterization of its behavior in zero-sum evolutionary games. We prove that, if and only if, the system has an interior Nash equilibrium, the dynamics exhibit Poincaré recurrence, i.e., almost all orbits come arbitrary close to their initial cond…

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…

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 …

遍历 $\mathbb{Z}^d$ 作用的原始平均、方向扩张性和定量扭曲回复性

Primitive Averages, Directional Expansivity, and Quantitative Twisted Recurrence for Ergodic $\mathbb{Z}^d$-Actions

本文为保概率 $\mathbb{Z}^d$ 作用建立了原始向量平均的 $L^2$ 极限公式，并给出了方向扩张集具有高下密度的谱条件，进而证明了扭曲多重回复定理的定量版本。

Nil Bohr$_0$-sets, Poincaré recurrence and generalized polynomials

The problem which can be viewed as the higher order version of an old question concerning Bohr sets is investigated: for any $d\in \N$ does the collection of $\{n\in \Z: S\cap (S-n)\cap...\cap (S-dn)\neq \emptyset\}$ with $S$ syndetic coincide with that of Nil$_d$ Bohr$_0$-sets? In this paper it is proved that Nil$_d$ Bohr$_0$-sets could be characterized via generalized polynomials, and applying this result one side of the problem could be answered affirmatively: for any Nil$_d$ Bohr$_0$-set $A$, there exists a syndetic set $S$ such that $A\supset \{n\in \Z: S\cap (S-n)\cap...\cap (S-dn)\neq \…

Recurrence, dimensions and Lyapunov exponents

We show that the Poincaré return time of a typical cylinder is at least its length. For one dimensional maps we express the Lyapunov exponent and dimension via return times.

Recurrence of cocycles and stationary random walks

We survey distributional properties of $\mathbb{R}^d$-valued cocycles of finite measure preserving ergodic transformations (or, equivalently, of stationary random walks in $\mathbb{R}^d$) which determine recurrence or transience.

Hyperbolicity and recurrence in dynamical systems: a survey of recent results

We discuss selected topics of current research interest in the theory of dynamical systems, with emphasis on dimension theory, multifractal analysis, and quantitative recurrence. The topics include the quantitative versus the qualitative behavior of Poincaré recurrence, the product structure of invariant measures and return times, the dimension of invariant sets and invariant measures, the complexity of the level sets of local quantities from the point of view of Hausdorff dimension, and the conditional variational principles as well as their applications to problems in number theory. We prese…

Some open problems on multiple ergodic averages

We survey some recent developments and give a list of open problems regarding multiple recurrence and convergence phenomena of $\mathbb{Z}^d$ actions in ergodic theory and related applications in combinatorics and number theory.

Online Optimization in Games via Control Theory: Connecting Regret, Passivity and Poincaré Recurrence

We present a novel control-theoretic understanding of online optimization and learning in games, via the notion of passivity. Passivity is a fundamental concept in control theory, which abstracts energy conservation and dissipation in physical systems. It has become a standard tool in analysis of general feedback systems, to which game dynamics belong. Our starting point is to show that all continuous-time Follow-the-Regularized-Leader (FTRL) dynamics, which include the well-known Replicator Dynamic, are lossless, i.e. it is passive with no energy dissipation. Interestingly, we prove that pass…

A note on the algebraic growth rate of Poincaré series for Kleinian groups

In this note we employ infinite ergodic theory to derive estimates for the algebraic growth rate of the Poincaré series for a Kleinian group at its critical exponent of convergence.

两类逐点遍历定理的统一方法：双重递归与返回时间

A Unified Approach to Two Pointwise Ergodic Theorems: Double Recurrence and Return Times

本研究提出统一方法，结合停时与度量熵，将Bourgain双重递归定理与返回时间定理推广到Kronecker序列整数部分，证明两类双线性遍历平均的几乎处处收敛性且收敛集对所有有理数γ一致。

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.

Spherical Recurrence and locally isometric embeddings of trees into positive density subsets of $\mathbb{Z}^d$

Magyar has shown that if $B \subset \mathbb{Z}^d$ has positive upper density $(d \geq 5)$, then the set of squared distances $\{ \|b_1-b_2 \|^2 \text{ }: \text{ } b_1,b_2 \in B \}$ contains an infinitely long arithmetic progression, whose period depends only on the upper density of $B$. We extend this result by showing that $B$ contains locally isometrically embedded copies of every tree with edge lengths in some given arithmetic progression (whose period depends only on the upper density of $B$ and the number of vertices of the sought tree). In particular, $B$ contains all chains of elements …

关于 $1$-有界乘性权的齐次遍历双线性平均

On the homogeneous ergodic bilinear averages with $1$-bounded multiplicative weights

本文推广了Bourgain双重回归定理和遍历Bourgain-Sarnak定理，证明非周期$1$-有界乘性权下齐次遍历双线性平均几乎处处收敛于零，并给出关键证明要素。

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 $\…