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On the length of an external branch in the Beta-coalescent
Jean-Stephane Dhersin 1, 2, Fabian Freund 3, Arno Siri-Jegousse 4, Linglong Yuan 1, 2
(08/01/2012)

In this paper, we consider Beta$(2-{\alpha},{\alpha})$ (with $1<{\alpha}<2$) and related ${\Lambda}$-coalescents. If $T^{(n)}$ denotes the length of an external branch of the $n$-coalescent, we prove the convergence of $n^{{\alpha}-1}T^{(n)}$ when $n$ tends to $ \infty $, and give the limit. To this aim, we give asymptotics for the number $\sigma^{(n)}$ of collisions which occur in the $n$-coalescent until the end of the chosen external branch, and for the block counting process associated with the $n$-coalescent.
1 :  Institut Galilée (IG)
Université Paris XIII - Paris Nord
2 :  Laboratoire Analyse, Géométrie et Application (LAGA)
CNRS : UMR7539 – Université Paris XIII - Paris Nord – Université Paris VIII - Vincennes Saint-Denis
3 :  Institute of Plant Breeding, Seed Science and Population Genetics
University of Hohenheim
4 :  Centro de Investigación en Matemáticas (CIMAT)
University of Guanajuato
Mathématiques/Probabilités
Coalescent process – Beta-coalescent – external branch – block counting process – recursive construction
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