Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados

TWO-VALUED ENSEMBLE OF THE GAUSSIAN FREE FIELD.

Event Date: Sep 15, 2016 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

ABSTRACT: The goal of this talk is to understand thin local sets of the continuous Gaussian free filed (GFF) in a domain of R^2, whose corresponding harmonic function takes only two values. We give a characterization of these sets and use it to show that in some sense they are maximal in a bigger class of local sets, where we only ask the function to be bounded. Important corollaries of this work are new constructions of the Conformal Loop Ensemble CLE_4 and a new perspective on the two known couplings between CLE_4 and the GFF. Joint work wiht JUHAN ARU and WENDELIN...

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Limiting laws for some integrated processes

Event Date: Aug 11, 2016 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

Resumen: The study of limiting laws, or penalizations, of a given process may be seen (in some sense) as a way to condition a probability law by an a.s. infinite random variable. The systematic study of such problems started in 2006 with a series of papers by Roynette, Vallois and Yor who looked at Brownian motion perturbed by several examples of functionals. These works were then generalized to many families of processes: random walks, Lévy processes, linear diffusions… We shall present here some examples of penalization of a non-Markov process, i.e. the integrated Brownian motion, by its...

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Phase Transitions on the Long Range Ising Models in presence of an random external field

Event Date: Jul 25, 2016 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

Resumen: We study the ferromagnetic one-dimensiosnal Random Field Ising Model with (RFIM) in presence of an external random field. The interaction between two spins decays as $d^{\alpha-2}$ where $d$ is the distance between two sites and $\alpha \in [0,1/2)$ is a parameter of the model. We consider an external random field on $\mathbb{Z}$ with independent but not identically distributed random variables. Specifically for each $i \in \mathbb{Z}$, the distribution of $h_i$ is $P[h_i=\pm \theta(1+|i|)^{-\nu/2}]$. This work, whose main goal is the study of the existence of a phase transition at...

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The log-Sobolev inequality for unbounded spin systems on the lattice. & Scaling limit of subcritical contact process.

Event Date: Jun 13, 2016 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

PRIMERA PARTE: Expositor: Ioannis Papageorgiou (UBA) Titulo: The log-Sobolev inequality for unbounded spin systems on the lattice. Resumen: A criterion will be presented for the log-Sobolev inequality for unbounded spin systems on the lattice with non-quadratic interactions. This is a joint work with Takis Konstantopoulos (Uppsala) and James Inglis (INRIA). Furthermore, in the case of quadratic interactions, a perturbation result for the inequality will be presented. SEGUNDA PARTE: Expositora: Aurelia Deshayes (UBA) Titulo: Scaling limit of subcritical contact process Resumen: I will talk...

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Percolation in hyperbolic space: the non-uniqueness phase.

Event Date: Nov 30, 1999 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

Resumen: We consider Bernoulli percolation on Cayley graphs of reflection groups in the 3-dimensional hyperbolic space H^3 corresponding to a large class of Coxeter polyhedra. In such setting, we prove the existence of a non-empty no-uniqueness percolation phase, i.e., that p_c<p_u. It means that for some values of the percolation parameter there are a.s. infinitely many infinite components in the percolation subgraph. If time permits, I will present a sketch for the case of a right angled compact polyhedron with at least 18 faces.

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Terrorists never congregate in even numbers (or: some strange results in fragmentation-coalescence)

Event Date: Jan 12, 2016 in Núcleo Modelos Estocásticos de Sistemas Complejos y Desordenados, Seminars

Abstract:   We analyse a class of fragmentation-coalescence processes defined on finite systems of particles organised into clusters. Coalescent events merge multiple clusters simultaneously to form a single larger cluster, while fragmentation breaks up a cluster into a collection of singletons. Under mild conditions on the coalescence rates, we show that the distribution of cluster sizes becomes non-random in the large-scale limit. Moreover, we discover that, in the limit of small fragmentation rate, these processes exhibit a universal heavy tailed distribution with exponent 3/2. In...

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