Exceptionally small balls in stable trees
[Boules exceptionnellement petites dans les arbres stables]
Bulletin de la Société Mathématique de France, Tome 142 (2014) no. 2, pp. 223-254

The γ-stable trees are random measured compact metric spaces that appear as the scaling limit of Galton-Watson trees whose offspring distribution lies in a γ-stable domain, γ(1,2]. They form a specific class of Lévy trees (introduced by Le Gall and Le Jan in [24]) and the Brownian case γ=2 corresponds to Aldous Continuum Random Tree (CRT). In this paper, we study fine properties of the mass measure, that is the natural measure on γ-stable trees. We first discuss the minimum of the mass measure of balls with radius r and we show that this quantity is of order rγγ-1(log1/r)-1γ-1. We think that no similar result holds true for the maximum of the mass measure of balls with radius r, except in the Brownian case: when γ=2, we prove that this quantity is of order r2log1/r. In addition, we compute the exact constant for the lower local density of the mass measure (and the upper one for the CRT), which continues previous results from [9, 10, 13].

Les arbres γ-stables sont des espaces métriques compacts à mesure aléatoire qui apparaissent en tant que limite de mise à l'échelle d'arbres de Galton-Watson dont les distributions sont situées dans un domaine γ-stable, γ]1,2]. Ils forment une class spécifique des arbres de Lévy (introduite par Le Gall et Le Jan dans [24]) et le cas brownien γ=2 correspond aux arbres aléatoires du continuum d'Aldous (CRT). Dans cet article nous étudions les propriétés fines de la mesure de masse, qui est la mesure naturelle des arbres γ-stables. Nous discutons d'abord le minimum de la mesure de masse des boules de rayon r et nous montrons que cette quantité est de l'ordre de rγγ-1(log1/r)-1γ-1. Nous pensons qu'aucun résultat similaire n'est vrai pour le maximum des mesures de masse de boule de rayon r, sauf dans le cas brownien : quand γ=2 nous montrons que cette quantité est de l'ordre de r2log1/r. D'autre part, nous calculons la constante exacte de la densité local inférieure de la mesure de masse (et la supérieure pour le CRT), à la suite de résultats précédents de [9, 10, 13].

Publié le :
DOI : 10.24033/bsmf.2664
Classification : 60G57, 60J80, 28A78
Keywords: Continuum random tree, Lévy trees, stable trees, mass measure, small balls.
Mots-clés : Arbre aléatoire du continuum, arbres de Lévy, arbres stables, mesure de masse, petites boules.
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Duquesne, Thomas; Wang, Guanying. Exceptionally small balls in stable trees. Bulletin de la Société Mathématique de France, Tome 142 (2014) no. 2, pp. 223-254. doi: 10.24033/bsmf.2664

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