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Pré-Publication, Document De Travail Année : 2016

HARMONIC MOMENTS AND LARGE DEVIATIONS FOR A SUPERCRITICAL BRANCHING PROCESS IN A RANDOM ENVIRONMENT

Résumé

Let $(Z_n)$ be a supercritical branching process in an independent and identically distributed random environment $\xi$. We study the asymptotic of the harmonic moments $\mathbb{E}\left[Z_n^{-r} | Z_0=k \right]$ of order $r>0$ as $n \to \infty$. We exhibit a phase transition with the critical value $r_k>0$ determined by the equation $\mathbb E p_1^k = \mathbb E m_0^{-r_k},$ where $m_0=\sum_{k=0}^\infty k p_k$ with $p_k=\mathbb P(Z_1=k | \xi),$ assuming that $p_0=0.$ Contrary to the constant environment case (the Galton-Watson case), this critical value is different from that for the existence of the harmonic moments of $W=\lim_{n\to\infty} Z_n / \mathbb E (Z_n|\xi).$ The aforementioned phase transition is linked to that for the rate function of the lower large deviation for $Z_n$. As an application, we obtain a lower large deviation result for $Z_n$ under weaker conditions than in previous works and give a new expression of the rate function. We also improve an earlier result about the convergence rate in the central limit theorem for $W-W_n,$ and find an equivalence for the large deviation probabilities of the ratio $Z_{n+1} / Z_n$.
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Dates et versions

hal-01357340 , version 1 (29-08-2016)

Identifiants

  • HAL Id : hal-01357340 , version 1

Citer

Ion Grama, Quansheng Liu, Eric Miqueu. HARMONIC MOMENTS AND LARGE DEVIATIONS FOR A SUPERCRITICAL BRANCHING PROCESS IN A RANDOM ENVIRONMENT. 2016. ⟨hal-01357340⟩
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