Limit theorems for discrete multitype branching processes counted with a characteristic

Abstract

For a discrete time multitype supercritical Galton–Watson process (Zn)n∈N and corresponding genealogical tree T, we associate a new discrete time process (ZnΦ)n∈N such that, for each n∈N, the contribution of each individual u∈T to ZnΦ is determined by a (random) characteristic Φ evaluated at the age of u at time n. In other words, ZnΦ is obtained by summing over all u∈T the corresponding contributions Φu, where (Φu)u∈T are i.i.d. copies of Φ. Such processes are known in the literature under the name of Crump–Mode–Jagers (CMJ) processes counted with characteristicΦ. We derive a LLN and a CLT for the process (ZnΦ)n∈N in the discrete time setting, and in particular, we show a dichotomy in its limit behavior. By applying our main result, we also obtain a generalization of the results in Kesten and Stigum (1966).