Laws of Large Numbers for the Occupation Time of an Age-Dependent Critical Binary Branching System

The occupation time of an age-dependent branching particle system in $\Rd$ is considered, where the initial population is a Poisson random field and the particles are subject to symmetric $\alpha$-stable migration, critical binary branching and random lifetimes. Two regimes of lifetime distributions are considered: lifetimes with finite mean and lifetimes belonging to the normal domain of attraction of a $\gamma$-stable law, $\gamma\in(0,1)$. It is shown that in dimensions $d>\alpha\gamma$ for the heavy-tailed lifetimes case, and $d>\alpha$ for finite mean lifetimes, the occupation time proccess satisfies a strong law of large numbers.