Existence and multiplicity of stable bound states for the nonlinear Klein-Gordon equation

We are interested in the problem of existence of soliton-like solutions for the nonlinear Klein-Gordon equation. In particular we study some necessary and sufficient conditions on the nonlinear term to obtain solitons of a given charge. We remark that the conditions we consider can be easily verified. Moreover we show that multiplicity of solitons of the same charge is guaranteed by the "shape" of the nonlinear term for equations on $\R^{N}$, hence without appealing to topological or geometrical properties of the domain.Comment: 18 page

The Algorithmic Information Content for randomly perturbed systems

In this paper we prove estimates on the behaviour of the Kolmogorov-Sinai entropy relative to a partition for randomly perturbed dynamical systems. Our estimates use the entropy for the unperturbed system and are obtained using the notion of Algorithmic Information Content. The main result is an extension of known results to study time series obtained by the observation of real systems.Comment: 17 pages, 1 figur

Solitons in gauge theories: existence and dependence on the charge

In this paper we review recent results on the existence of non-topological solitons in classical relativistic nonlinear field theories. We follow the Coleman approach, which is based on the existence of two conservation laws, energy and charge. In particular we show that under mild assumptions on the nonlinear term it is possible to prove the existence of solitons for a set of admissible charges. This set has been studied for the nonlinear Klein-Gordon equation, and in this paper we state new results in this direction for the Klein-Gordon-Maxwell system.Comment: 18 pages, proceedings of the "International Workshop on Variational Problems and PDEs", Sao Paulo, September 201

Computational information for the logistic map at the chaos threshold

We study the logistic map $f(x)=\lambda x(1-x)$ on the unit square at the chaos threshold. By using the methods of symbolic dynamics, the information content of an orbit of a dynamical system is defined as the Algorithmic Information Content (AIC) of a symbolic sequence. We give results for the behaviour of the AIC for the logistic map. Since the AIC is not a computable function we use, as approximation of the AIC, a notion of information content given by the length of the string after it has been compressed by a compression algorithm, and in particular we introduce a new compression algorithm called CASToRe. The information content is then used to characterise the chaotic behaviour.Comment: 23 pages, 3 figures, changed conten

Escape rates for the Farey map with approximated holes

We study the escape rate for the Farey map, an infinite measure preserving system, with a hole including the indifferent fixed point. Due to the ergodic properties of the map, the standard theoretical approaches to this problem cannot be applied. To overcome this difficulties we propose here to consider approximations of the hole by means of real analytic functions. We introduce a particular family of approximations and study numerically the behavior of the escape rate for "shrinking" approximated holes. The results suggest that the scaling of the escape rate depends on the chosen approximation, but "converges" to the behavior found for piecewise linear approximations of the map in \cite{KM}.Comment: 11 pages, 4 figure

A renormalization approach to irrational rotations

We introduce a renormalization procedure which allows us to study in a unified and concise way different properties of the irrational rotations on the unit circle $\beta \mapsto \set{\alpha+\beta}$, \alpha \in \R\setminus \Q. In particular we obtain sharp results for the diffusion of the walk on $\Z$ generated by the location of points of the sequence $\{n\alpha +\beta\}$ on a binary partition of the unit interval. Finally we give some applications of our method.Comment: 27 page