A second order asymptotic expansion in the local limit theorem for a simple branching random walk in [formula omitted]

Abstract

Consider a branching random walk, where the underlying branching mechanism is governed by a Galton–Watson process and the migration of particles by a simple random walk in Zd. Denote by Zn(z) the number of particles of generation n located at site z∈Zd. We give the second order asymptotic expansion for Zn(z). The higher order expansion can be derived by using our method here. As a by-product, we give the second order expansion for a simple random walk on Zd, which is used in the proof of the main theorem and is of independent interest.