Let S=\{p_1, \ldots , p_r,\infty \}$S=\{p_1, \ldots , p_r,\infty \}$ for prime integers p_1, \ldots , p_r.$p_1, \ldots , p_r.$ Let X be an S-adic compact nilmanifold, equipped with the unique translation-invariant probability measure \mu .$\mu .$ We characterize the countable groups \Gamma $\Gamma$ of automorphisms of X for which the Koopman representation \kappa $\kappa$ on L^2(X,\mu )$L^2(X,\mu )$ has a spectral gap. More specifically, let Y be the maximal quotient solenoid of X (thus, Y is a finite-dimensional, connected, compact abelian group). We show that \kappa $\kappa$ does not have a spectral gap if and only if there exists a \Gamma $\Gamma$-invariant proper subsolenoid of Y on which \Gamma $\Gamma$ acts as a virtually abelian group,

We study infinite systems of mean field weakly coupled intermittent maps in the Pomeau–Manneville scenario. We prove that the coupled system admits a unique ‘physical’ stationary state, to which all absolutely continuous states converge. Moreover, we show that suitably regular states converge polynomially.

We look at constructions of aperiodic subshifts of finite type (SFTs) on fundamental groups of graph of groups. In particular, we prove that all generalized Baumslag-Solitar groups (GBS) admit a strongly aperiodic SFT. Our proof is based on a structural theorem by Whyte and on two constructions of strongly aperiodic SFTs on \mathbb {F}_n\times \mathbb {Z}$\mathbb {F}_n\times \mathbb {Z}$ and BS(m,n)$BS(m,n)$ of our own. Our two constructions rely on a path-folding technique that lifts an SFT on \mathbb {Z}^2$\mathbb {Z}^2$ inside an SFT on \mathbb {F}_n\times \mathbb {Z}$\mathbb {F}_n\times \mathbb {Z}$ or an SFT on the hyperbolic plane inside an SFT on BS(m,n)$BS(m,n)$. In the case of \mathbb {F}_n\times \mathbb {Z}$\mathbb {F}_n\times \mathbb {Z}$, the path folding technique also preserves minimality, so that we get minimal strongly aperiodic SFTs on unimodular GBS groups.

Let l\in \mathbb {N}_{\ge 1}$l\in \mathbb {N}_{\ge 1}$ and \alpha : \mathbb {Z}^l\rightarrow \text {Aut}(\mathscr {N})$\alpha : \mathbb {Z}^l\rightarrow \text {Aut}(\mathscr {N})$ be an action of \mathbb {Z}^l$\mathbb {Z}^l$ by automorphisms on a compact nilmanifold \mathscr{N}$\mathscr{N}$. We assume the action of every \alpha (z)$\alpha (z)$ is ergodic for z\in \mathbb {Z}^l\smallsetminus \{0\}$z\in \mathbb {Z}^l\smallsetminus \{0\}$ and show that \alpha $\alpha$ satisfies exponential n-mixing for any integer n\geq 2$n\geq 2$. This extends the results of Gorodnik and Spatzier [Mixing properties of commuting nilmanifold automorphisms. Acta Math. 215 (2015), 127–159].

We show that the Hausdorff dimension of any slice of the graph of the Takagi function is bounded above by the Assouad dimension of the graph minus one, and that the bound is sharp. The result is deduced from a statement on more general self-affine sets, which is of independent interest. We also prove that Marstrand’s slicing theorem on the graph of the Takagi function extends to all slices if and only if the upper pointwise dimension of every projection of the length measure on the x-axis lifted to the graph is at least one.

We present a modified version of the well-known geometric Lorenz attractor. It consists of a C^1$C^1$ open set {\mathcal O}${\mathcal O}$ of vector fields in {\mathbb R}^3${\mathbb R}^3$ having an attracting region {\mathcal U}${\mathcal U}$ satisfying three properties. Namely, a unique singularity \sigma $\sigma$; a unique attractor \Lambda $\Lambda$ including the singular point and the maximal invariant in {\mathcal U}${\mathcal U}$ has at most two chain recurrence classes, which are \Lambda $\Lambda$ and (at most) one hyperbolic horseshoe. The horseshoe and the singular attractor have a collision along with the union of 2$2$ codimension 1$1$ submanifolds which split {\mathcal O}${\mathcal O}$ into three regions. By crossing this collision locus, the attractor and the horseshoe may merge into a two-sided Lorenz attractor, or they may exchange their nature: the Lorenz attractor expels the singular point \sigma $\sigma$ and becomes a horseshoe, and the horseshoe absorbs \sigma $\sigma$ becoming a Lorenz attractor.

We introduce a notion of sensitivity with respect to a continuous real-valued bounded map which provides a sufficient condition for a continuous transformation, acting on a Baire metric space, to exhibit a Baire generic subset of points with historic behavior (also known as irregular points). The applications of this criterion recover, and extend, several known theorems on the genericity of the irregular set, in addition to yielding a number of new results, including information on the irregular set of geodesic flows, in both negative and non-positive curvature, and semigroup actions.

To any k-dimensional subspace of \mathbb {Q}^n$\mathbb {Q}^n$ one can naturally associate a point in the Grassmannian \mathrm {Gr}_{n,k}(\mathbb {R})$\mathrm {Gr}_{n,k}(\mathbb {R})$ and two shapes of lattices of rank k and n-k$n-k$, respectively. These lattices originate by intersecting the k-dimensional subspace and its orthogonal with the lattice \mathbb {Z}^n$\mathbb {Z}^n$. Using unipotent dynamics, we prove simultaneous equidistribution of all of these objects under congruence conditions when (k,n) \neq (2,4)$(k,n) \neq (2,4)$.

In this paper, we consider random dynamical systems formed by concatenating maps acting on the unit interval [0,1]$[0,1]$ in an independent and identically distributed (i.i.d.) fashion. Considered as a stationary Markov process, the random dynamical system possesses a unique stationary measure \nu $\nu$. We consider a class of non-square-integrable observables \phi $\phi$, mostly of form \phi (x)=d(x,x_0)^{-{1}/{\alpha }}$\phi (x)=d(x,x_0)^{-{1}/{\alpha }}$, where x_0$x_0$ is a non-recurrent point (in particular a non-periodic point) satisfying some other genericity conditions and, more generally, regularly varying observables with index \alpha \in (0,2)$\alpha \in (0,2)$. The two types of maps we concatenate are a class of piecewise C^2$C^2$ expanding maps and a class of intermittent maps possessing an indifferent fixed point at the origin. Under conditions on the dynamics and \alpha $\alpha$, we establish Poisson limit laws, convergence of scaled Birkhoff sums to a stable limit law, and functional stable limit laws in both the annealed and quenched case. The scaling constants for the limit laws for almost every quenched realization are the same as those of the annealed case and determined by \nu $\nu$. This is in contrast to the scalings in quenched central limit theorems where the centering constants depend in a critical way upon the realization and are not the same for almost every realization.

Inspired by the phase transition results for non-singular Gaussian actions introduced in [AIM19], we prove several phase transition results for non-singular Bernoulli actions. For generalized Bernoulli actions arising from groups acting on trees, we are able to give a very precise description of their ergodic-theoretical properties in terms of the Poincaré exponent of the group.

We define the co-spectral radius of inclusions {\mathcal S}\leq {\mathcal R}${\mathcal S}\leq {\mathcal R}$ of discrete, probability- measure-preserving equivalence relations as the sampling exponent of a generating random walk on the ambient relation. The co-spectral radius is analogous to the spectral radius for random walks on G/H$G/H$ for inclusion H\leq G$H\leq G$ of groups. For the proof, we develop a more general version of the 2–3 method we used in another work on the growth of unimodular random rooted trees. We use this method to show that the walk growth exists for an arbitrary unimodular random rooted graph of bounded degree. We also investigate how the co-spectral radius behaves for hyperfinite relations, and discuss new critical exponents for percolation that can be defined using the co-spectral radius.

We study stationary measures for iterated function systems (considered as random dynamical systems) consisting of two piecewise affine interval homeomorphisms, called Alsedà–Misiurewicz (AM) systems. We prove that for an open set of parameters, the unique non-atomic stationary measure for an AM system has Hausdorff dimension strictly smaller than 1$1$. In particular, we obtain singularity of these measures, answering partially a question of Alsedà and Misiurewicz [Random interval homeomorphisms. Publ. Mat. 58(suppl.) (2014), 15–36].

Recently, Benini et al showed that, in simply connected wandering domains of entire functions, all pairs of orbits behave in the same way relative to the hyperbolic metric, thus giving us our first insight into the general internal dynamics of such domains. The author proved in a recent paper [G. R. Ferreira. Multiply connected wandering domains of meromorphic functions: internal dynamics andconnectivity. J. Lond. Math. Soc. (2) 106 (2022), 1897–1919] that the same is not true for multiply connected wandering domains, a natural question is how inhomogeneous multiply connected wandering domains can be. We give an answer to this question, in that we show that uniform dynamics inside an open subset of the domain generalizes to the whole wandering domain. As an application of this result, we construct the first example of a meromorphic function with a semi-contracting infinitely connected wandering domain.

Given a locally finite graph \Gamma $\Gamma$, an amenable subgroup G of graph automorphisms acting freely and almost transitively on its vertices, and a G-invariant activity function \unicode{x3bb} $\unicode{x3bb}$, consider the free energy f_G(\Gamma ,\unicode{x3bb} )$f_G(\Gamma ,\unicode{x3bb} )$ of the hardcore model defined on the set of independent sets in \Gamma $\Gamma$ weighted by \unicode{x3bb} $\unicode{x3bb}$. Under the assumption that G is finitely generated and its word problem can be solved in exponential time, we define suitable ensembles of hardcore models and prove the following: if \|\unicode{x3bb} \|_\infty < \unicode{x3bb} _c(\Delta )$\|\unicode{x3bb} \|_\infty < \unicode{x3bb} _c(\Delta )$, there exists a randomized \epsilon $\epsilon$-additive approximation scheme for f_G(\Gamma ,\unicode{x3bb} )$f_G(\Gamma ,\unicode{x3bb} )$ that runs in time \mathrm {poly}((1+\epsilon ^{-1})\lvert \Gamma /G \rvert )$\mathrm {poly}((1+\epsilon ^{-1})\lvert \Gamma /G \rvert )$, where \unicode{x3bb} _c(\Delta )$\unicode{x3bb} _c(\Delta )$ denotes the critical activity on the \Delta $\Delta$-regular tree. In addition, if G has a finite index linearly ordered subgroup such that its algebraic past can be decided in exponential time, we show that the algorithm can be chosen to be deterministic. However, we observe that if \|\unicode{x3bb} \|_\infty> \unicode{x3bb} _c(\Delta )$\|\unicode{x3bb} \|_\infty> \unicode{x3bb} _c(\Delta )$, there is no efficient approximation scheme, unless \mathrm {NP} = \mathrm {RP}$\mathrm {NP} = \mathrm {RP}$. This recovers the computational phase transition for the partition function of the hardcore model on finite graphs and provides an extension to the infinite setting. As an application in symbolic dynamics, we use these results to develop efficient approximation algorithms for the topological entropy of subshifts of finite type with enough safe symbols, we obtain a representation formula of pressure in terms of random trees of self-avoiding walks, and we provide new conditions for the uniqueness of the measure of maximal entropy based on the connective constant of a particular associated graph.

We describe two kinds of regular invariant measures on the boundary path space \partial E$\partial E$ of a second countable topological graph E, which allows us to describe all extremal tracial weights on C^{*}(E)$C^{*}(E)$ which are not gauge-invariant. Using this description, we prove that all tracial weights on the C^{*}$^{*}$-algebra C^{*}(E)$C^{*}(E)$ of a second countable topological graph E are gauge-invariant when E is free. This in particular implies that all tracial weights on C^{*}(E)$C^{*}(E)$ are gauge-invariant when C^{*}(E)$C^{*}(E)$ is simple and separable.

In this paper, we study centrally symmetric Birkhoff billiard tables. We introduce a closed invariant set \mathcal {M}_{\mathcal {B}}$\mathcal {M}_{\mathcal {B}}$ consisting of locally maximizing orbits of the billiard map lying inside the region \mathcal {B}$\mathcal {B}$ bounded by two invariant curves of 4$4$-periodic orbits. We give an effective bound from above on the measure of this invariant set in terms of the isoperimetric defect of the curve. The equality case occurs if and only if the curve is a circle.

We prove that any strongly mixing action of a countable abelian group on a probability space has higher-order mixing properties. This is achieved via the utilization of \mathcal R$\mathcal R$-limits, a notion of convergence which is based on the classical Ramsey theorem. \mathcal R$\mathcal R$-limits are intrinsically connected with a new combinatorial notion of largeness which is similar to but has stronger properties than the classical notions of uniform density one and IP^*$^*$. While the main goal of this paper is to establish a universal property of strongly mixing actions of countable abelian groups, our results, when applied to {\mathbb {Z}}${\mathbb {Z}}$-actions, offer a new way of dealing with strongly mixing transformations. In particular, we obtain several new characterizations of strong mixing for {\mathbb {Z}}${\mathbb {Z}}$-actions, including a result which can be viewed as the analogue of the weak mixing of all orders property established by Furstenberg in the course of his proof of Szemerédi’s theorem. We also demonstrate the versatility of \mathcal R$\mathcal R$-limits by obtaining new characterizations of higher-order weak and mild mixing for actions of countable abelian groups.

We show that a class of higher-dimensional hyperbolic endomorphisms admit absolutely continuous invariant probabilities whose densities are regular and vary differentiably with respect to the dynamical system. The maps we consider are skew-products given by T(x,y) = (E (x), C(x,y))$T(x,y) = (E (x), C(x,y))$, where E is an expanding map of \mathbb {T}^u$\mathbb {T}^u$ and C is a contracting map on each fiber. If \inf |\!\det DT| \inf \| (D_yC)^{-1}\| ^{-2s}>1$\inf |\!\det DT| \inf \| (D_yC)^{-1}\| ^{-2s}>1$ for some {s<r-(({u+d})/{2}+1)}${s<r-(({u+d})/{2}+1)}$, r \geq 2$r \geq 2$, and T satisfies a transversality condition between overlaps of iterates of T (a condition which we prove to be C^r$C^r$-generic under mild assumptions), then the SRB measure \mu _T$\mu _T$ of T is absolutely continuous and its density h_T$h_T$ belongs to the Sobolev space H^s({\mathbb {T}}^u\times {\mathbb {R}}^d)$H^s({\mathbb {T}}^u\times {\mathbb {R}}^d)$. When s> {u}/{2}$s> {u}/{2}$, it is also valid that the density h_T$h_T$ is differentiable with respect to T. Similar results are proved for thermodynamical quantities for potentials close to the geometric potential.

We consider orthogonally invariant probability measures on \operatorname {\mathrm {GL}}_n(\mathbb {R})$\operatorname {\mathrm {GL}}_n(\mathbb {R})$ and compare the mean of the logs of the moduli of eigenvalues of the matrices with the Lyapunov exponents of random matrix products independently drawn with respect to the measure. We give a lower bound for the former in terms of the latter. The results are motivated by Dedieu and Shub [On random and mean exponents for unitarily invariant probability measures on \operatorname {\mathrm {GL}}_n(\mathbb {C})$\operatorname {\mathrm {GL}}_n(\mathbb {C})$. Astérisque 287 (2003), xvii, 1–18]. A novel feature of our treatment is the use of the theory of spherical polynomials in the proof of our main result.

We introduce the notions of returns and well-aligned sets for closed relations on compact metric spaces and then use them to obtain non-trivial sufficient conditions for such a relation to have non-zero entropy. In addition, we give a characterization of finite relations with non-zero entropy in terms of Li–Yorke and DC2 chaos.