Convergence of complex martingales in supercritical multi-type general branching processes in $L^q$ for $1 < q \leq 2$

Abstract

Nerman's martingale plays a central role in the law of large numbers for both, single- and multi-type, supercritical general branching processes. There are further, complex-valued Nerman-type martingales in the single-type process that figure in the finer fluctuations of these processes. We construct the analogous martingales for the process with finitely many types and give sufficient conditions for these martingales to converge in $L^q$ for $q \in (1,2]$.