## On the external branches of coalescents with multiple collisions.(English)Zbl 1285.60079

Summary: A recursion for the joint moments of the external branch lengths for coalescents with multiple collisions (lambda-coalescents) is provided. This recursion is used to derive asymptotic results as the sample size $$n$$ tends to infinity for the joint moments of the external branch lengths and for the moments of the total external branch length of the Bolthausen-Sznitman coalescent. These asymptotic results are based on a differential equation approach, which is as well useful to obtain exact solutions for the joint moments of the external branch lengths for the Bolthausen-Sznitman coalescent. The results for example show that the lengths of two randomly chosen external branches are positively correlated for the Bolthausen-Sznitman coalescent, whereas they are negatively correlated for the Kingman coalescent provided that $$n \geq 4$$.

### MSC:

 60J25 Continuous-time Markov processes on general state spaces 34E05 Asymptotic expansions of solutions to ordinary differential equations 60C05 Combinatorial probability 60J85 Applications of branching processes 92D15 Problems related to evolution 92D25 Population dynamics (general)
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