1969/06/01 by Walter L. Smith, William E. Wilkinson · 21 citations
Mathematics · Biochemistry, Genetics and Molecular Biology · #Stochastic processes and statistical mechanics #Diffusion and Search Dynamics #Mathematical Dynamics and Fractals
paper · doi:10.1214/aoms/1177697589
\ζn\ is a sequence of iid "environmental" variables in an abstract space Θ. Each point ζ ε Θ is associated with a pgf φζ(s). The branching process \Zn\ is defined as a Markov chain such that Z0 = k, a finite integer, and given Zn and ζn, Zn+1 is distributed as the sum of Zn iid random variables, each with pgf φζn(s). Set ξ(ζn) = φ'ζn(1) and assume that E|logξ(ζn)| < ∞. Then: (i) P\Zn = 0\ → 1 if E log ξ(ζn) \leqq 0; (ii) qk = def lim P\Zn = 0\ < 1 if E log ξ(ζn) > 0 and E|log (1 - φζn(0))| < ∞. Furthermore \qk\, k = 1, 2, ⋯, forms a moment sequence.