Unimodularity for multi-type Galton-Watson trees

Abstract

Fix $n\in\mathbb{N}$. Let $\mathbf{T}_n$ be the set of rooted trees $(T,o)$ whose vertices are labeled by elements of $\{1,...,n\}$. Let $ν$ be a strongly connected multi-type Galton-Watson measure. We give necessary and sufficient conditions for the existence of a measure $μ$ that is reversible for simple random walk on $\mathbf{T}_n$ and has the property that given the labels of the root and its neighbors, the descendant subtrees rooted at the neighbors of the root are independent multi-type Galton-Watson trees with conditional offspring distributions that are the same as the conditional offspring distributions of $ν$ when the types are $ν$ are ordered pairs of elements of $[n]$. If the types of $ν$ are given by the labels of vertices, then we give an explicit description of such $μ$.