We study the zero-temperature limit for Gibbs measures associated to Frenkel–Kontorova models on ${\left({ℝ}^d\right)}^{\mathbb{Z}}/{\mathbb{Z}}^d$. We prove that equilibrium states concentrate on configurations of minimal energy, and, in addition, must satisfy a variational principle involving metric entropy and Lyapunov exponents, a bit like in the Ruelle–Pesin inequality. Then we transpose the result to certain continuous-time stationary stochastic processes associated to the viscous Hamilton–Jacobi equation. As the viscosity vanishes, the...

Optimal stopping time problems for a risk process $U_t=u+ct-{\sum }_{n=0}^{N\left(t\right)}{X}_n$ where the number N(t) of losses up to time t is a general renewal process and the sequence of $X_i$’s represents successive losses are studied. N(t) and $X_i$’s are independent. Our goal is to maximize the expected return before the ruin time. The main results are closely related to those obtained by Boshuizen and Gouweleew [2].

Analizamos el problema de parada óptima con horizonte aleatorio en procesos de Markov con tiempo continuo. En concreto, estudiamos el caso en el que el horizonte es el tiempo de primera entrada en el interior de un cerrado B. Definimos las funciones B-excesivas y vemos su relación con el pago del problema de parada óptima. Posteriormente introducimos varios conjuntos, que aparecen de forma natural en el problema y que nos permiten caracterizar los dominios de parada. Por último consideramos el caso...

Dans cet article, nous pénalisons la loi d’une araignée brownienne ${\left(A_t\right)}_{t\ge 0}$ prenant ses valeurs dans un ensemble fini $E$ de demi-droites concourantes, avec un poids égal à $\frac{1}{Z_t}exp({\alpha }_{N_t}{X}_t+\gamma L_t)$, où $t$ est un réel positif, ${\left({\alpha }_k\right)}_{k\in E}$ une famille de réels indexés par $E$, $\gamma$ un paramètre réel, $X_t$ la distance de $A_t$ à l’origine, $N_t$ ($\in E$) la demi-droite sur laquelle se trouve $A_t$, $L_t$ le temps local de ${\left(X_s\right)}_{0\le s\le t}$ à l’origine, et $Z_t$ la constante de normalisation. Nous montrons que la famille des mesures de probabilité obtenue par ces pénalisations converge vers...

The paper is concerned with a stochastic delay predator-prey model under regime switching. Sufficient conditions for extinction and non-persistence in the mean of the system are established. The threshold between persistence and extinction is also obtained for each population. Some numerical simulations are introduced to support our main results.

Consider a strong Markov process in continuous time, taking values in some Polish state space. Recently, Douc et al. [Stoc. Proc. Appl. 119, (2009) 897–923] introduced verifiable conditions in terms of a supermartingale property implying an explicit control of modulated moments of hitting times. We show how this control can be translated into a control of polynomial moments of abstract regeneration times which are obtained by using the regeneration method of Nummelin, extended to the time-continuous...

Expected suprema of a function f observed along the paths of a nice Markov process define an excessive function, and in fact a potential if f vanishes at the boundary. Conversely, we show under mild regularity conditions that any potential admits a representation in terms of expected suprema. Moreover, we identify the maximal and the minimal representing function in terms of probabilistic potential theory. Our results are motivated by the work of El Karoui and Meziou (2006) on the max-plus decomposition...

Un théorème classique exprime qu’à partir d’un semi-groupe $(P^t{)}_{t\ge 0}$ d’opérateurs sur l’espace des fonctions continues tendant vers 0 à l’infini, $P^{s+t}=P^t$, $P^s\ge 0$, $P^{t}l=1$, $t\to P^{t}f$ continue, $P^0=I$, on peut construire un processus markovien “standard”, à trajectoires réglées et continues à droite, quasi-continu à gauche ; l’espace des états $E$ est supposé localement compact à base dénombrable d’ouverts. Nous supposons ici que l’espace des états est seulement universellement mesurable dans un souslinien complètement régulier ; le processus...