Pruning of CRT-sub-trees

TL;DR

This paper investigates the properties and representations of a two-parameter pruning process on Lévy trees, establishing its construction, marginals, and the distribution of key times, and showing the equivalence of certain super-critical Lévy trees.

Contribution

It provides a detailed construction and analysis of a two-parameter pruning process on Lévy trees, including its marginals, representations, and key distributional results, linking continuous and discrete models.

Findings

Construction and marginals of the pruning process are established.

Representation of the process forward and backward in time is provided.

Distribution of the ascension time and the tree at that time is characterized.

Abstract

We study the pruning process developed by Abraham and Delmas (2012) on the discrete Galton-Watson sub-trees of the L\'{e}vy tree which are obtained by considering the minimal sub-tree connecting the root and leaves chosen uniformly at rate $\lambda$, see Duquesne and Le Gall (2002). The tree-valued process, as $\lambda$ increases, has been studied by Duquesne and Winkel (2007). Notice that we have a tree-valued process indexed by two parameters the pruning parameter $\theta$ and the intensity $\lambda$. Our main results are: construction and marginals of the pruning process, representation of the pruning process (forward in time that is as $\theta$ increases) and description of the growing process (backward in time that is as $\theta$ decreases) and distribution of the ascension time (or explosion time of the backward process) as well as the tree at the ascension time. A by-product of our result is that the super-critical L\'{e}vy trees independently introduced by Abraham and Delmas (2012) and Duquesne and Winkel (2007) coincide. This work is also related to the pruning of discrete Galton-Watson trees studied by Abraham, Delmas and He (2012).