Mertens' theorem for toral automorphisms

某些部分双曲环面自同构的中心化子分类与刚性

Centralizer classification and rigidity for some partially hyperbolic toral automorphisms

本文研究环面自同构邻近微分同胚的中心化子分类与刚性，在低维及高维情形下证明了中心化子较大时的光滑共轭刚性，并对辛情形给出有限指数分类。

Smooth local rigidity for hyperbolic toral automorphisms

We study the regularity of a conjugacy $H$ between a hyperbolic toral automorphism $A$ and its smooth perturbation $f$ We show that if $H$ is weakly differentiable then it is $C^{1+Hölder}$ and, if $A$ is also weakly irreducible, then $H$ is $C^\infty$. As a part of the proof, we establish results of independent interest on Hölder continuity of a measurable conjugacy between linear cocycles over a hyperbolic system. As a corollary, we improve regularity of the conjugacy to $C^\infty$ in prior local rigidity results.

Symmetries and reversing symmetries of toral automorphisms

Toral automorphisms, represented by unimodular integer matrices, are investigated with respect to their symmetries and reversing symmetries. We characterize the symmetry groups of GL(n,Z) matrices with simple spectrum through their connection with unit groups in orders of algebraic number fields. For the question of reversibility, we derive necessary conditions in terms of the characteristic polynomial and the polynomial invariants. We also briefly discuss extensions to (reversing) symmetries within affine transformations, to PGL(n,Z) matrices, and to the more general setting of integer matric…

Diophantine properties of groups of toral automorphisms

We prove sharp estimates in a shrinking target problem for the action of an arbitrary subgroup $Γ$ of $SL_2(\mathbb{Z})$ on the 2-torus. This can also be viewed as a non-commutative Diophantine approximation problem. The methods require constructing spectrally optimal random walks on groups acting properly cocompactly on Gromov hyperbolic spaces. Additionally, using Fourier analysis we give estimates for the same problem in higher dimensions.

环面自同构的全局光滑刚性

Global smooth rigidity for toral automorphisms

本文证明非常弱不可约双曲或遍历部分双曲环面自同构的$C^1$或$C^{1+\text{Hölder}}$共轭自动提升为$C^\infty$，从而改进局部与全局刚性结果。

Local rigidity for hyperbolic toral automorphisms

We consider a hyperbolic toral automorphism $L$ and its $C^1$-small perturbation $f$. It is well-known that $f$ is Anosov and topologically conjugate to $L$, but a conjugacy $H$ is only Hölder continuous in general. We discuss conditions for smoothness of $H$, such as conjugacy of the periodic data of $f$ and $L$, coincidence of their Lyapunov exponents, and weaker regularity of $H$, and we summarize questions, results, and techniques in this area. Then we introduce our new results: if $H$ is weakly differentiable then it is $C^{1+\text{Hölder}}$ and, if $L$ is also weakly irreducible, then $H…

Topological Self-joinings of Cartan Actions by Toral Automorphisms

We show that if $r\geq 3$ and $α$ is a faithful $Z^r$-Cartan action on a torus $T^d$ by automorphisms, then any closed subset of $(T^d)^2$ which is invariant and topologically transitive under the diagonal $\bZ^r$-action by $α$ is homogeneous, in the sense that it is either the full torus $(T^d)^2$, or a finite set of rational points, or a finite disjoint union of parallel translates of some d-dimensional invariant subtorus. A counterexample is constructed for the rank 2 case.

Local rigidity of Lyapunov spectrum for toral automorphisms

We study the regularity of the conjugacy between an Anosov automorphism $L$ of a torus and its small perturbation. We assume that $L$ has no more than two eigenvalues of the same modulus and that $L^4$ is irreducible over $\mathbb Q$. We consider a volume-preserving $C^1$-small perturbation $f$ of $L$. We show that if Lyapunov exponents of $f$ with respect to the volume are the same as Lyapunov exponents of $L$, then $f$ is $C^{1+\text{Hölder}}$ conjugate to $L$. Further, we establish a similar result for irreducible partially hyperbolic automorphisms with two-dimensional center bundle.

A Profinite Group Invariant for Hyperbolic Toral Automorphisms

For a hyperbolic toral automorphism, we construct a profinite completion of an isomorphic copy of the homoclinic group of its right action using isomorphic copies of the periodic data of its left action. The resulting profinite group has a natural module structure over a ring determined by the right action of the hyperbolic toral automorphism. This module is an invariant of conjugacy that provides means in which to characterize when two similar hyperbolic toral automorphisms are conjugate or not. In particular, this shows for two similar hyperbolic toral automorphisms with module isomorphic le…

Rigidity of Commutative Non-hyperbolic Actions by Toral Automorphisms

Berend gives necessary and sufficient conditions on a $Z^r$-action $α$ on a torus $T^d$ by toral automorphisms in order for every orbit be either finite or dense. One of these conditions is that on every common eigendirection of the $Z^r$-action there is an element $\mathbf n \in Z^r$ so that $α^\mathbf n$ expands this direction. In this paper, we investigate what happens when this condition is removed; more generally, we consider a partial orbit $\{α^\mathbf n.x : \mathbf n \in Ω\}$ where $Ω$ is a set of elements which acts approximately as the identity on a given set of eigendirections. This…

Global rigidity of certain abelian actions by toral automorphisms

We prove global rigidity results for some linear abelian actions on tori. The type of actions we deal with includes in particular maximal rank semisimple actions on $\T^N$.

仿射环面自同构的可逆性与对称性

Reversibility and symmetry of affine toral automorphisms

研究二维环面上仿射自同构的可逆性与强可逆性，基于矩阵A和平移向量a导出可逆性判据，并利用Pick定理给出存在不动点的几何条件。

Exponential Decay of Correlations for Randomly Chosen Hyperbolic Toral Automorphisms

We consider pairs of toral automorphisms (A,B) satisfying an invariant cone property. At each iteration, A acts with probability p and B with probability 1-p. We prove exponential decay of correlations for a class of Holder continuous observables.

Positive Voiculescu-Brown entropy in noncommutative toral automorphisms

We show that the Voiculescu-Brown entropy of a noncommutative toral automorphism arising from a matrix S in GL(d,Z) is at least half the value of the topological entropy of the corresponding classical toral automorphism. We also obtain some information concerning the positivity of local Voiculescu-Brown entropy with respect to single unitaries. In particular we show that if S has no roots of unity as eigenvalues then the local Voiculescu-Brown entropy with respect to every product of canonical unitaries is positive, and also that in the presence of completely positive CNT entropy the unital ve…

$C^*$-algebras associated with asymptotic equivalence relations defined by hyperbolic toral automorphisms

We study the $C^*$-algebras of the étale groupoids defined by the asymptotic equivalence relations for hyperbolic automorphisms on the two-dimensional torus. The algebras are proved to be four-dimensional non-commutative tori by an explicit numerical computation. The ranges of the unique tracial states of its $K_0$-groups of the $C^*$-algebras are described in terms of the hyperbolic matrices of the automorphisms on the torus.

受扰环面自同构的 Lyapunov 指数的解析性

Analiticity of the Lyapunov exponents of perturbed toral automorphisms

本文研究了环面上解析 Anosov 微分同胚在解析扰动下的动力系统，证明了不变子空间的分裂可通过部分共轭扩展至扰动系统，并得出非退化 Lyapunov 指数是扰动的解析函数。

Sequences from zero entropy noncommutative toral automorphisms and Sarnak Conjecture

In this paper we study $C^*$-algebra version of Sarnak Conjecture for noncommutative toral automorphisms. Let $A_Θ$ be a noncommutative torus and $α_Θ$ be the noncommutative toral automorphism arising from a matrix $S\in GL(d,\mathbb{Z})$. We show that if the Voiculescu-Brown entropy of $α_Θ$ is zero, then the sequence $\{ρ(α_Θ^nu)\}_{n\in \mathbb{Z}}$ is a sum of a nilsequence and a zero-density-sequence, where $u\in A_Θ$ and $ρ$ is any state on $A_Θ$. Then by a result of Green and Tao, this sequence is linearly disjoint from the Möbius function.

Counting Berg partitions

We call a Markov partition of a two dimensional hyperbolic toral automorphism a Berg partition if it contains just two rectangles. We describe all Berg partitions for a given hyperbolic toral automorphism. In particular there are exactly (k + n + l + m)/2 nonequivalent Berg partitions with the same connectivity matrix (k, l, m, n).

Symbolic representations of nonexpansive group automorphisms

If $α$ is an irreducible nonexpansive ergodic automorphism of a compact abelian group $X$ (such as an irreducible nonhyperbolic ergodic toral automorphism), then $α$ has no finite or infinite state Markov partitions, and there are no nontrivial continuous embeddings of Markov shifts in $X$. In spite of this we are able to construct a symbolic space $V$ and a class of shift-invariant probability measures on $V$ each of which corresponds to an $α$-invariant probability measure on $X$. Moreover, every $α$-invariant probability measure on $X$ arises essentially in this way. The last part of the pa…

Quenched CLT for random toral automorphism

We establish a quenched Central Limit Theorem (CLT) for a smooth observable of random sequences of iterated linear hyperbolic maps on the torus. To this end we also obtain an annealed CLT for the same system. We show that, almost surely, the variance of the quenched system is the same as for the annealed system. Our technique is the study of the transfer operator on an anisotropic Banach space specifically tailored to use the cone condition satisfied by the maps.

Central limit theorem for commutative semigroups of toral endomorphisms

Let $\Cal S$ be an abelian finitely generated semigroup of endomorphisms of a probability space $(Ω, {\Cal A}, μ)$, with $(T_1, ..., T_d)$ a system of generators in ${\Cal S}$. Given an increasing sequence of domains $(D_n) \subset \N^d$, a question is the convergence in distribution of the normalized sequence $|D_n|^{-\frac12} \sum_{{\k} \, \in D_n} \, f \circ T^{\,{\k}}$, for $f \in L^2_0(μ)$, where $T^{\k}= T_1^{k_1} ... T_d^{k_d}$, ${\k}= (k_1, ..., k_d) \in {\N}^d$. After a preliminary spectral study when the action of $\Cal S$ has a Lebesgue spectrum, we consider $\N^d$- or $\Z^d$-action…

双曲环面自同构的四元数扩张

Quaternionic Extensions of Hyperbolic Toral Automorphisms

本研究构造了SU(2)×SU(2)上提升双曲环面自同构的实解析微分同胚，分析了其不变集、周期点性质、特征簇作用及本征流收敛性，排除了Anosov双曲性。

Local Conjugacy of Irreducible Hyperbolic Toral Automorphisms

This paper is dedicated to the conjugacy problem in $GL(n,\Z)$ and its connection with algebraic number theory. This connection may be summed up in the Latimer-MacDuffee-Taussky Theorem, which, in a very broad sense, identifies the conjugacy relation in $GL(n,\Z)$ with the relation of arithmetic equivalence between certain ideals of algebraic numbers. The main purpouse is to clarify the link between a weaker relation between ideals, weak equivalence, and local conjugacy in $GL(n,\Z)$, i.e., the conjugacy of $GL(n,\Z)$ matrices in the groups $GL(n,\Z_{p})$ of invertible matrices over the $p$-ad…

A note on the dynamical zeta function of general toral endomorphisms

It is well-known that the Artin-Mazur dynamical zeta function of a hyperbolic or quasi-hyperbolic toral automorphism is a rational function, which can be calculated in terms of the eigenvalues of the corresponding integer matrix. We give an elementary proof of this fact that extends to the case of general toral endomorphisms without change. The result is a closed formula that can be calculated by integer arithmetic only. We also address the functional equation and the relation between the Artin-Mazur and Lefschetz zeta functions.

Automorphisms with exotic orbit growth

We exhibit continua on two different growth scales in the dynamical Mertens' theorem for ergodic automorphisms of one-dimensional solenoids.

具有二维中心的遍历环面自同构的扰动的拓扑中心化子

Topological centralizers of perturbations of ergodic toral automorphisms with two dimensional center

该研究针对具有二维中心的遍历环面自同构的C²²邻域内的微分同胚，证明了二分性结果，明确了其可达性与拓扑共轭的等价条件，给出了其中心化子的结构。

Pseudo-Anosov mappings and toral automorphisms

For every irreducible automorphism $ϕ\in\text{SL}_3({\mathbb Z})$ of the $3$-torus, for which the product of the expanding eigenvalues is positive, we construct a pseudo-Anosov mapping $f$ of an associated surface, semi-conjugate and almost-isomorphic to $ϕ$, whose stretch factor is the product of the expanding eigenvalues of $ϕ$. This shows that any norm-$1$ cubic Pisot number occurs as the stretch factor of a pseudo-Anosov mapping, proving a conjecture of Fried in degree $3$. A similar construction works for the $4$-torus on condition that $ϕ$ has exactly two eigenvalues outside the unit cir…

不可约环面自同构的全局周期数据刚性

Global periodic-data rigidity for irreducible toral automorphisms

针对线性化不可约的环面Anosov微分同胚，证明若所有周期点的导数与线性化共轭，则Franks-Manning共轭是C^{1+Hölder}的，即周期数据完全刻画全局刚性。

非平稳马尔可夫划分与多维连续分数算法

Nonstationary Markov Partitions and Multidimensional Continued Fraction Algorithms

本文研究了非平稳马尔可夫划分与多维连续分数算法的关联，通过皮索型条件证明了非平稳动力系统的双曲性，并构建了基于符号动力系统的非平稳边移位模型。

Reversing Symmetry Groups of Cat Maps

Toral automorphisms are widely used (discrete) dynamical systems, the perhaps most prominent example (in 2D) being Arnold's cat map. Given such an automorphism M, its symmetries (i.e. all automorphisms that commute with M) and reversing symmetries (i.e. all automorphisms that conjugate M into its inverse) can be determined by means of number theoretic tools. Here, the case of GL(2,Z) is presented and the possible (reversing) symmetry groups are completely classified. Extensions to affine mappings and to k-(reversing) symmetries (i.e. (reversing) symmetries of the k-th power of M), and applicat…

A note on reversibility and Pell equations

We consider hyperbolic toral automorphisms which are reversible with respect to a linear area-preserving involution. We will prove that within this context reversibility is linked to a generalized Pell equation whose solutions we will analyze. Additionally, we will verify to what extent reversibility is a common feature and characterize the generic setting.

Ergodic universality of some topological dynamical systems

The Krieger generator theorem says that every invertible ergodic measure-preserving system with finite measure-theoretic entropy can be embedded into a full shift with strictly greater topological entropy. We extend Krieger's theorem to include toral automorphisms, and more generally, any topological dynamical system on a compact metric space that satisfies almost weak specification, asymptotic entropy expansiveness, and the small boundary property. As a corollary, one obtains a complete solution to a natural generalization of an open problem in Halmos's 1956 book regarding an isomorphism inva…

Arithmetic Dynamics

This survey paper is aimed to describe a relatively new branch of symbolic dynamics which we call Arithmetic Dynamics. It deals with explicit arithmetic expansions of reals and vectors that have a "dynamical" sense. This means precisely that they (semi-) conjugate a given continuous (or measure-preserving) dynamical system and a symbolic one. The classes of dynamical systems and their codings considered in the paper involve: (1) Beta-expansions, i.e., the radix expansions in non-integer bases; (2) "Rotational" expansions which arise in the problem of encoding of irrational rotations of the cir…

Ergodic properties of Erdös measure, the entropy of the goldenshift, and related problems

We define a two-sided analog of Erdös measure on the space of two-sided expansions with respect to the powers of the golden ratio, or, equivalently, the Erdös measure on the 2-torus. We construct the transformation (goldenshift) preserving both Erdös and Lebesgue measures on $\Bbb T^2$ which is the induced automorphism with respect to the ordinary shift (or the corresponding Fibonacci toral automorphism) and proves to be Bernoulli with respect to both measures in question. This provides a direct way to obtain formulas for the entropy dimension of the Erdös measure on the interval, its entropy …