Behavior near the extinction time in self-similar fragmentations I: The stable case

The stable fragmentation with index of self-similarity α ∈ [-1/2, 0) is derived by looking at the masses of the subtrees formed by discarding the parts of a (1+α)-1-stable continuum random tree below height t, for t ≥ 0. We give a detailed limiting description of the distribution of such a fragmentation, (F (t), t ≥ 0), as it approaches its time of extinction, ζ. In particular, we show that t 1/αF((ζ - t)+) converges in distribution as t → 0 to a non-trivial limit. In order to prove this, we go further and describe the limiting behavior of (a) an excursion of the stable height process (conditioned to have length 1) as it approaches its maximum; (b) the collection of open intervals where the excursion is above a certain level; and (c) the ranked sequence of lengths of these intervals. Our principal tool is excursion theory. We also consider the last fragment to disappear and show that, with the same time and space scalings, it has a limiting distribution given in terms of a certain size-biased version of the law of ζ. In addition, we prove that the logarithms of the sizes of the largest fragment and last fragment to disappear, at time (ζ - t)+, rescaled by log(t), converge almost surely to the constant -1/α as t → 0. © Association des Publications de l'Institut Henri Poincaré, 2010.