arXiv subjects
Publications and source records attributed to Helder Vilarinho.
We obtain estimates on the decay of correlations, Central Limit Theorem and Large Deviations for dynamical systems admitting an induced weak Gibbs--Markov map, for larger classes of observables with weaker regularity than Hölder, characterized by suitable moduli of continuity.
In this paper, we introduce generalized dichotomies for nonautonomous random linear dynamical systems acting on arbitrary Banach spaces, and obtain their complete characterization in terms of an appropriate admissibility property. These generalized dichotomies are associated to growth rates satisfying mild conditions and they include the standard exponential behavior as a very particular case. As a nontrivial application, we establish the robustness property of such dichotomies under small (linear) perturbations.
For small perturbations of linear Random Dynamical Systems evolving on a Banach space and exhibiting a generalized form of trichotomy, we prove the existence of invariant center manifolds, both in continuous and discrete-time. Furthermore, we provide several illustrative examples.
Our main goal is to understand the stability of second order linear homogeneous differential equations $\ddot x(t)+α(t)\dot x(t)+β(t)x(t)=0$ for $C^0$-generic values of the variable parameters $α(t)$ and $β(t)$. For that we embed the problem into the framework of the general theory of continuous-time linear cocycles induced by the random ODE $\ddot x(t)+α(φ^t(ω))\dot x(t)+β(φ^t(ω))x(t)=0$, where the coefficients $α$ and $β$ evolve along the $φ^t$-orbit for $ω\in M$, and $φ^t: M\to M$ is a flow defined on a compact Hausdorff space $M$ preserving a probability measure $μ$. Considering $y=\dot x$, the above random ODE can be rewritten as $\dot X=A(φ^t (ω))X$, with $X=(x,y)^\top$, having a kinetic linear cocycle as fundamental solution. We prove that for a $C^0$-generic choice of parameters $α$ and $β$ and for $μ$-almost all $ω\in M$ either the Lyapunov exponents of the linear cocycle are equal ($λ_1(ω)=λ_2(ω)$), or else the orbit of $ω$ displays a dominated splitting. Applying to dissipative systems ($α<0$) we obtain a dichotomy: either $λ_1(ω)=λ_2(ω)<0$, attesting the stability of the solution of the random ODE above, or else the orbit of $ω$ displays a dominated splitting. Applying to frictionless systems ($α=0$) we obtain a dichotomy: either $λ_1(ω)=λ_2(ω)=0$, attesting the asymptotic neutrality of the solution of the random ODE above, or else the orbit of $ω$ displays a hyperbolic splitting attesting the \emph{uniform} instability of the solution of the ODE above. This last result implies also an analog result for the 1-d continuous aperiodic Schrödinger equation. Furthermore, all results hold for $L^\infty$-generic parameters $α$ and $β$.
In this article, we address the decay of correlations for dynamical systems that admit an induced weak Gibbs Markov map (not necessarily full branch). Our approach generalizes L.-S. Young's coupling arguments to estimate the decay of correlations for the tower map of the induced weak Gibbs Markov map in terms of the tail of the return time function. For that we initially discuss how to ensure the mixing property of the tower map. Additionally, we yield results concerning the Central Limit Theorem and Large Deviations.
Given an ergodic flow $φ^t\colon M\rightarrow M$ defined on a probability space $M$ we study a family of continuous-time kinetic linear cocycles associated to the solutions of the second order linear homogeneous differential equations $\ddot x +α(φ^t(ω))\dot x+β(φ^t(ω))x=0$, where the parameters $α,β$ evolve along the $φ^t$-orbit of $ω\in M$. Our main result states that for a generic subset of kinetic continuous-time linear cocycles, where generic means a Baire second category with respect to an $L^p$-like topology on the infinitesimal generator, the Lyapunov spectrum is trivial.
In the present paper we prove that densely, with respect to an $L^p$-like topology, the Lyapunov exponents associated to linear continuous-time cocycles $Φ:\mathbb{R}\times M\to \text{GL}(2,\mathbb{R})$ induced by second order linear homogeneous differential equations $\ddot x+α(φ^t(ω))\dot x+β(φ^t(ω))x=0$ are almost everywhere distinct. The coefficients $α,β$ evolve along the $φ^t$-orbit for $ω\in M$ and $φ^t: M\to M$ is an ergodic flow defined on a probability space. We also obtain the corresponding version for the frictionless equation $\ddot x+β(φ^t(ω))x=0$ and for a Schrödinger equation $\ddot x+(E-Q(φ^t(ω)))x=0$, inducing a cocycle $Φ:\mathbb{R}\times M\to \text{SL}(2,\mathbb{R})$.
We consider a nonautonomous eco-epidemiological model with general functions for predation on infected and uninfected preys as well as general functions associated to the vital dynamics of the susceptible prey and predator populations. We obtain persistence and extinction results for the infected prey based on assumptions on systems related to the dynamics in the absence of infected preys. We apply our results to eco-epidemiological models constructed from predator-prey models existent in the literature. Some illustrative simulation is undertaken.
We prove the existence of measurable invariant manifolds for small perturbations of linear Random Dynamical Systems evolving on a Banach space and admitting a general type of dichotomy, both for continuous and discrete time. Moreover, the asymptotic behavior in the invariant manifold is similar to the one of the linear Random Dynamical System.
We consider random perturbations of a general eco-epidemiological model. We prove the existence of a global random attractor, the persistence of susceptibles preys and provide conditions for the simultaneous extinction of infectives and predators. We also discuss the dynamics of the corresponding random epidemiological $SI$ and predator-prey models. We obtain for this cases a global random attractor, prove the prevalence of susceptibles/preys and provide conditions for the extinctions of infectives/predators.
Using Mickens nonstandard method, we obtain a discrete family of nonautonomous eco-epidemiological models that include general functions corresponding to the predation of the infected and uninfected preys. We obtain results on the persistence and extinction of the infected preys assuming that the bi-dimensional predator-prey subsystem that describes the dynamics in the absence of the infection satisfies some assumptions. Some examples and simulations are undertaken to illustrate our results.
We consider random perturbations of a topologically transitive local diffeomorphism of a Riemannian manifold. We show that if an absolutely continuous ergodic stationary measures is expanding (all Lyapunov exponents positive), then there is a random Gibbs-Markov-Young structure which can be used to lift that measure. We also prove that if the original map admits a finite number of expanding invariant measures then the stationary measures of a sufficiently small stochastic perturbation are expanding.
We consider random perturbations of non-uniformly expanding maps, possibly having a non-degenerate critical set. We prove that, if the Lebesgue measure of the set of points failing the non-uniform expansion or the slow recurrence to the critical set at a certain time, for almost all random orbits, decays in a (stretched) exponential fashion, then the decay of correlations along random orbits is stretched exponential, up to some waiting time. As applications, we obtain almost sure stretched exponential decay of random correlations for Viana maps, as for a class of non-uniformly expanding local diffeomorphisms and a quadratic family of interval maps.
In this paper we generalize [3] and prove that the class of accessible and saddle-conservative cocycles (a wide class which includes cocycles evolving in GL(d,R), SL(d,R) and Sp(d,R) Lp-densely have a simple spectrum. We also generalize [3, 1] and prove that for an Lp-residual subset of accessible cocycles we have a one-point spectrum, by using a different approach of the one given in [3]. Finally, we show that the linear differential system versions of previous results also hold and give some applications.
We give an application of a topological dynamics version of multidimensional Brown's lemma to tiling theory: given a tiling of an Euclidean space and a finite geometric pattern of points $F$, one can find a patch such that, for each scale factor $λ$, there is a vector $\vec{t}_λ$ so that copies of this patch appear in the tilling "nearly" centered on $λF+\vec{t}_λ$ once we allow "bounded perturbations" in the structure of the homothetic copies of $F$. Furthermore, we introduce a new unifying setting for the study of tiling spaces which allows rather general group "actions" on patches and we discuss the local isomorphism property of tilings within this setting.
Given a finite set ${S_1...,S_k}$ of substitution maps acting on a certain finite number (up to translations) of tiles in $\rd$, we consider the multi-substitution tiling space associated to each sequence $\bar a\in {1,...,k}^{\mathbb{N}}$. The action by translations on such spaces gives rise to uniquely ergodic dynamical systems. In this paper we investigate the rate of convergence for ergodic limits of patches frequencies and prove that these limits vary continuously with $\bar a$.
We consider random perturbations of discrete-time dynamical systems. We give sufficient conditions for the stochastic stability of certain classes of maps, in a strong sense. This improves the main result in J. F. Alves, V. Araujo, Random perturbations of non-uniformly expanding maps, Asterisque 286 (2003), 25--62, where it was proved the convergence of the stationary measures of the random process to the SRB measure of the initial system in the weak* topology. Here, under slightly weaker assumptions on the random perturbations, we obtain a stronger version of stochastic stability: convergence of the densities of the stationary measures to the density of the SRB measure of the unperturbed system in the L1-norm. As an application of our results we obtain strong stochastic stability for two classes of non-uniformly expanding maps. The first one is an open class of local diffeomorphisms introduced in J. F. Alves, C. Bonatti, M. Viana, SRB measures for partially hyperbolic systems whose central direction is mostly expanding, Invent. Math. 140 (2000), 351--398, and the second one the class of Viana maps.