Sharp approximation and hitting times for stochastic invasion processes

Vincent Bansaye (1, 2) , Xavier Erny (1) , Sylvie Méléard (1, 2)

1 CMAP - Centre de Mathématiques Appliquées - Ecole Polytechnique
2 MERGE - Mathématiques pour l’évolution, la reproduction, la croissance et l’émergence

We are interested in the invasion phase for stochastic processes with interactions when a single mutant with positive fitness arrives in a resident population at equilibrium. By a now classic approach, the first stage of the invasion is well approximated by a branching process. The macroscopic phase, when the mutant population is of the same order of the resident population, is described by the limiting dynamical system. We obtain sharper estimates and capture the intermediate mesoscopic phase for the invasive population. It allows us to characterize the hitting times of thresholds, which inherit a large variance from the first stages. These issues are motivated in particular by quantifying times to reach critical values for cancer population or epidemics.

Mots clés: Branching process; Dynamical system; Stochastic processes approximation; Hitting times approximation

Domaines: Probabilités [math.PR]

Vincent Bansaye, Xavier Erny, Sylvie Méléard. Sharp approximation and hitting times for stochastic invasion processes. 2023. ⟨hal-03915479v3⟩