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Impulsive Dynamical Systems

Everaldo de Mello Bonotto

Abstract:

In this talk, we present the concept of impulsive dynamical systems. Moreover, we establish sufficient conditions to obtain the existence of a global attractor.

Lyapunov exponents, the problem of regularity

El Hadji Yaya Tall

Abstract:

The study of Lyapunov exponent goes back to the stability theory for differential equations developed in the doctoral thesis of Aleksandr M. Lyapunov, in the late 19th century, since then, it grew into a very broad area and active field in ergodic theory and dynamical systems, with several outstanding problems and applications.  In the early 80’s, Ricardo Mañé observed that the Lyapunov exponents of continuous 2-dimensional cocycle can be cancelled by arbitrarily small perturbation of the cocycle. The proof of this observation was completed by Jairo Bochi.

In 2010, Carlos Bocker and Marcelo Viana have proven that the Lyapunov exponent of random 2-dimensional cocycle vary always continuously with respect to the probability distribution. This result was also extended in arbitrarily dimensional by Artur Avila, Alex Eskin and Marcelo Viana. Recently Marcelo Viana and myself have proven that the Lyapunov exponents of random 2-dimensional cocycle are Hölder continuous functions of the underlying probability distribution at each point with simple Lyapunov spectrum. Moreover, they are log-Hölder continuous at every point.

I will first discuss the problem of continuity and give some ideas and results about Hölder continuity.

Foliated Brownian motion and Harmonic measures.

Diego Sebastian Ledesma

Abstract:

For a foliated manifold, we present the construction of foliated Brownian motion via stochastic calculus adapted to foliation. The stochastic approach together with a proposed foliated vector calculus provide a natural method to work on harmonic measures. Also, we show a decomposition of the Laplacian in terms of the foliated and basic Laplacians, a characterization of totally invariant measures and a differential equation for the density of harmonic measures.

Contribuições ao problema da continuidade para expoentes de Lyapunov

Adriana Sánchez Chavarría

Abstract:

Varios autores tem estudado o problema da continuidade dos expoentes de Lyapunov. Exemplo disto são os trabalhos de Bochi-Mañé, Bocker-Viana e Backes, Butler e Brown. No primeiro, os autores mostraram que todo SL(2)-cociclo contínuo que não é uniformemente hiperbólico pode ser aproximado por outro com expoentes nulos. Os outros dois mostram continuidade dos expoentes para o produto aleatorio de matrices com medidas de soporte compacto e quando a base é um deslocamento de tipo finito respetivamente.

Nesta palestra explicarei estos resultados e as principais diferenças respeto a os casos parcialmente hiperbólico e medidas com soporte não compacto.

Geometric Anosov Actions

Uirá Norberto Matos de Almeida

Abstract:

There exists a long standing conjecture about the algebricity of Anosov actions of higher ranked abelian groups. On this talk, we present some work in progress on a especial cases of this conjecture, based on a similar work about the algebricity of Anosov Flows on dimension 5, by Young Fang. We consider an Anosov action with smooth invariant stable and unstable bundles that preserves a pseudo-metric, and present some partial results on the algebricity of such actions.

Onset of diffusion in the kicked Harper model

Fabio Tal

Abstract:

We study a standard two-parameter family of area-preserving torus diffeomorphisms, known as the kicked Harper model in theoretical physics, by a combination of topological arguments and KAM-theory. We concentrate on the structure of the parameter sets where the rotation set has empty and non-empty interior, respectively, and describe their qualitative properties and scaling behaviour both for small and large parameters. This confirms numerical observations about the onset of diffusion in the physics literature. As a byproduct, we obtain the continuity of the rotation set within the class of Hamiltonian torus homeomorphisms.
This is Joint work w. T. Jäger and A. Koropecki

Lift problem and equilibrium states

Vilton Pinheiro

Abstract:

In the first lecture we will talk about the problem of lifting a measure to an induced map. We will give a necessary and sufficient condition for a measure to be liftable as well as a condition for the lift to be ergodic and unique.

The second lecture will be dedicated to construct induced maps well adapted to a given ergodic invariant probability with all its Lyapunov exponents being positive (expanding measure).

Finally, in the third lecture, we will discuss about equilibrium states on the support of an ergodic invariant expanding probability. In particular, (1)  we will show that Viana maps have one and only one probability maximizing their entropy and (2) we will analyze the existence and uniqueness of the equilibrium states for Hölder potentials at high temperature.

Renormalization of multicritical circle maps

Gabriela Estevez

Abstract:

In this talk, we will present the renormalization operator for multicritical circle maps and we will give certain conditions to get rigidity results, for almost all irrational rotation number. This is a joint work with Pablo Guarino (UFF-Brazil).

Hamiltonian stability on open surfaces

Roland Rabanal

Abstract:

We extend to open surfaces with simple singularities the theorem proposed by Xavier Jarque and Zbigniew Nitecki for Hamiltonian flows in the plane that are structurally stable among Hamiltonian flows. We describe the Hamiltonian dynamics on open surfaces by presenting characterization theorems for Hamiltonian stability and some natural consequences.

On positive metric entropy problem

Dmitry Turaev

Abstract:

We show that any smooth area-preserving diffeomorphism of a two-dimensional surface which has an elliptic fixed point can be perturbed to one exhibiting a chaotic island whose metric entropy is positive, the perturbation is small in the C-infinity topology. This proves a conjecture by Herman stating that the identity map of the disk can be perturbed to a conservative diffeomorphism with positive metric entropy. This implies also that the Chirikov standard map for large and small parameter values can be arbitrarily well approximated by a conservative diffeomorphism with a positive metric entropy (a weak version of Sinai’s positive metric entropy conjecture). We argue that these results question the relevance of the notions of metric entropy and Lyapunov exponents to the grand problem of understanding the Hamiltonian chaos. This is a joint work with Pierre Berger.