Surviving particles for subcritical branching processes in random environment

Vincent Bansaye (1)

1 LPMA - Laboratoire de Probabilités et Modèles Aléatoires

The asymptotic behavior of a subcritical Branching Process in Random Environment (BPRE) starting with several particles depends on whether the BPRE is strongly subcritical (SS), intermediate subcritical (IS) or weakly subcritical (WS). %Descendances of particles for BPRE are not independent. In the (SS+IS) case, the asymptotic probability of survival is proportional to the initial number of particles, and conditionally on the survival of the population, only one initial particle survives $a.s.$ These two properties do not hold in the (WS) case and different asymptotics are established, which require new results on random walks with negative drift. We provide an interpretation of these results by characterizing the sequence of environments selected when we condition on the survival of particles. This also raises the problem of the dependence of the Yaglom quasistationary distributions on the initial number of particles and the asymptotic behavior of the Q-process associated with a subcritical BPRE.

Mots clés: Branching process in random environment (BPRE). Yaglom distribution. Q-process. Random walk with negative drift.; Branching process in random environment (BPRE). Yaglom distribution. Q-process. Random walk with negative drift

Domaines: Probabilités [math.PR]

Vincent Bansaye. Surviving particles for subcritical branching processes in random environment. 2008. ⟨hal-00270541v3⟩