arXiv subjects

A. T. Baraviera

Publications and source records attributed to A. T. Baraviera.

5 recordsLinked to original sources

arXiv2014

On the dynamics of a rational semigroup on a convolution measure algebra

We are going to study the dynamical properties of the rational semigroup $Q_{t}(μ)$ where $Q_{t}(μ)= (1-t) μ* (1- t μ)^{-1},$ for $t \in [0,1)$, that is defined for $μ\in \mathcal{P}(G)$, the set of Borel probabilities over $(G, \cdot)$ an abelian compact topological group where we define the \textbf{convolution}, $ν* μ\in \mathcal{P}(G)$, as usual for a group $\int f d(ν* μ)= \int \int f(xy) dν(x) dμ(y),$ then $(\mathcal{P}(G), *)$ became a $\textbf{convolution measure algebra}$ (CM-algebra). We investigate several properties for this semigroup (as the Stable Manifold Theorem, Asymptotic behavior, invariant sets, differential properties, stationary points, etc) and how they are related with the Choquet-Deny equation. As an application we give a complete description of this semigroup for finite abelian groups.

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arXiv2013

Ergodic optimization, zero temperature limits and the max-plus algebra

Lecture notes of a course at the Brazilian Mathematical Colloquium. We review some basic notions in ergodic theory and thermodynamic formalism, as well as introductory results in the context of max-plus algebra, in order to exhibit some properties of equilibrium measures when temperature goes to zero.

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arXiv2012

Formulas for Lyapunov exponents

We derive a series summation formula for the average logarithm norm of the action of a matrix on the projective space. This formula is shown to be useful to evaluate some Lyapunov exponents of random $\SL$-matrix cocycles, which include a special class for which H. Furstenberg had provided an explicit integral formula.

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arXiv2011

On the general one-dimensional XY Model: positive and zero temperature, selection and non-selection

We consider $(M,d)$ a connected and compact manifold and we denote by $\mathcal{B}_i$ the Bernoulli space $M^{\Z}$ of sequences represented by $$x=(... x_{-3},x_{-2},x_{-1},x_0,x_1,x_2,x_3,...),$$ where $x_i$ belongs to the space (alphabet) $M$. The case where $M=\mathbb{S}^1$, the unit circle, is of particular interest here. The analogous problem in the one-dimensional lattice $\mathbb{N}$ is also considered. %In this case we consider the potential $A: {\cal B}=M^\mathbb{N} \to \mathbb{R}.$ Let $A: \mathcal{B}_i \rar \R$ be an {\it observable} or {\it potential} defined in the Bernoulli space $\mathcal{B}_i$. The potential $A$ describes an interaction between sites in the one-dimensional lattice $M^\mathbb{Z}$. Given a temperature $T$, we analyze the main properties of the Gibbs state $\hatμ_{\frac{1}{T} A}$ which is a certain probability measure over ${\cal B}_i$. We denote this setting "the general XY model". In order to do our analysis we consider the Ruelle operator associated to $\frac{1}{T} A$, and, we get in this procedure the main eigenfunction $ψ_{\frac{1}{T} A}$. Later, we analyze selection problems when temperature goes to zero: a) existence, or not, of the limit (on the uniform convergence) $$V:=\lim_{T\to 0} T\, \log(ψ_{\frac{1}{T} A}),\,\,\,\,\text{a question about selection of subaction},$$ and, b) existence, or not, of the limit (on the weak$^*$ sense) $$\tildeμ:=\lim_{T\to 0} \hatμ_{\frac{1}{T}\, A},\,\,\,\,\text{a question about selection of measure}.$$ The existence of subactions and other properties of Ergodic Optimization are also considered.

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arXiv2011

On the selection of subaction and measure for a subclass of potentials defined by P. Walters

Suppose $σ$ is the shift acting on Bernoulli space $X=\{0,1\}^\mathbb{N}$, and, consider a fixed function $f:X \to \mathbb{R}$, under the Waters's conditions (defined in a paper in ETDS 2007). For each real value $t\geq 0$ we consider the Ruelle Operator $L_{tf}$. We are interested in the main eigenfunction $h_t$ of $L_{tf}$, and, the main eigenmeasure $ν_t$, for the dual operator $L_{tf}^*$, which we consider normalized in such way $h_t(0^\infty)=1$, and, $\int h_t \,d\,ν_t=1, \forall t>0$. We denote $μ_t= h_t ν_t$ the Gibbs state for the potential $t\, f$. By selection of a subaction $V$, when the temperature goes to zero (or, $t\to \infty$), we mean the existence of the limit $$V:=\lim_{t\to\infty}\frac{1}{t}\log(h_{t}).$$ By selection of a measure $μ$, when the temperature goes to zero (or, $t\to \infty$), we mean the existence of the limit (in the weak$^*$ sense) $$μ:=\lim_{t\to\infty} μ_t.$$ We present a large family of non-trivial examples of $f$ where the selection of measure exists. These $f$ belong to a sub-class of potentials introduced by P. Walters. In this case, explicit expressions for the selected $V$ can be obtained for a certain large family of potentials.

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