Vertex reinforced branching random walks and generalized time-dependent Polya urns

We consider a class of infinite critical tree-indexed random walks on $\mathbb Z$, where the motion of particles is subject to vertex reinforcement.

We mainly focus on the strong reinforcement regime, where we expect the process to localize almost surely on two sites.

Part of our analysis includes the study of a time-dependent generalized Pólya urn process, where the number of draws at each step is prescribed by a sequence $(\sigma_n)_{n\ge 1}$ of arbitrary positive integers, and the probability to pick a ball of a given color is proportional to a function of the {\it number} of balls of that color.

In particular for bounded sequences $(\sigma_n)_{n\ge 1}$, we recover Rubin's characterization for the fixation of one color.