Abstract:
We consider a Galton–Watson branching process with particles of two
types in which particles of type one produce both particles of types one and
two, and particles of type two generate offsprings of only type two. It is
known that if both types are critical, then, for a process that is initiated
at time $0$ by a single type-one particle, the number of particles of type
two at time $n$ (provided that the process is not degenerate by this time) is
proportional to $n$. We find the asymptotics of the probability that the
number of type-two particles at time $n$ is of the order $o(n) $ (provided
that the process is not degenerate by this time).
Keywords:reduced branching process, population size, local limit theorem.