Quenched law of large numbers for branching Brownian motion in a random medium

TL;DR

This paper establishes a quenched law of large numbers for branching Brownian motion in a random medium with obstacles, showing reduced spreading speed and a dichotomy in local growth for general diffusions.

Contribution

It proves a quenched law of large numbers for branching Brownian motion in random obstacles and extends results to general diffusions and offspring distributions.

Findings

Branching Brownian motion spreads less quickly with obstacles

Quenched law of large numbers holds for all dimensions

Dichotomy in local growth independent of obstacle intensity

Abstract

We study a spatial branching model, where the underlying motion is $d$-dimensional ($d\ge1$) Brownian motion and the branching rate is affected by a random collection of reproduction suppressing sets dubbed mild obstacles. The main result of this paper is the quenched law of large numbers for the population for all $d\ge1$. We also show that the branching Brownian motion with mild obstacles spreads less quickly than ordinary branching Brownian motion by giving an upper estimate on its speed. When the underlying motion is an arbitrary diffusion process, we obtain a dichotomy for the quenched local growth that is independent of the Poissonian intensity. More general offspring distributions (beyond the dyadic one considered in the main theorems) as well as mild obstacle models for superprocesses are also discussed.