A quadratic ancestor inequality for spanning trees

Abstract

We introduce a quadratic ancestor inequality for weighted spanning trees on finite undirected graphs and give two applications. First, for every finite $n$-vertex transitive graph, the expected distance in its uniform spanning tree (UST) between two independent uniform vertices is at least $\sqrt{n}-1$, resolving a conjecture in [Benjamini--Kozma, Comm. Math. Phys. 259 (2005), 257--286]. Second, we prove that the growth exponent of three-dimensional loop-erased random walk (LERW) is at least 3/2.