Maximum Agreement Subtrees and Hölder homeomorphisms between Brownian trees

Abstract

We prove that the size of the largest common subtree between two uniform, independent, leaf-labelled random binary trees of size $n$ is typically less than $n^{1/2-\epsilon }$ for some $\epsilon >0$. Our proof relies on the coupling between discrete random trees and the Brownian tree and on a recursive decomposition of the Brownian tree due to Aldous. Along the way, we also show that almost surely, there is no $(1-\epsilon )$-Hölder homeomorphism between two independent copies of the Brownian tree.

32 pages, 5 figures