A discontinuous percolation phase transition on the hierarchical lattice

TL;DR

This paper characterizes the precise conditions under which long-range percolation on hierarchical lattices exhibits discontinuous phase transitions, identifying a critical kernel threshold involving a logarithmic correction.

Contribution

It extends classical percolation results to hierarchical lattices, establishing the exact kernel order that induces discontinuous phase transitions, including a hierarchical analogue of a longstanding conjecture.

Findings

Discontinuous phase transition occurs at a specific kernel order involving a logarithmic correction.

No phase transition occurs for kernels of smaller order.

Provides an exact formula for the infinite cluster density at the transition point.

Abstract

For long-range percolation on $\mathbb{Z}$ with translation-invariant edge kernel $J$, it is a classical theorem of Aizenman and Newman (1986) that the phase transition is discontinuous when $J(x,y)$ is of order $|x-y|^{-2}$ and that there is no phase transition at all when $J(x,y)=o(|x-y|^{-2})$. We prove a strengthened version of this theorem for the hierarchical lattice, where the relevant threshold is at $|x-y|^{-2d} \log\log |x-y|$ rather than $|x-y|^{-2}$: There is a continuous phase transition for kernels of larger order, a discontinuous phase transition for kernels of exactly this order, and no phase transition at all for kernels of smaller order. As such, $|x-y|^{-2d} \log\log |x-y|$ is essentially the \emph{only} kernel that produces a discontinuous phase transition. We also prove a hierarchical analogue of the ``$M^2\beta=1$'' conjecture of Imbrie and Newman (1988), which gives an exact formula for the density of the infinite cluster at the point of discontinuous phase transition and remains open in the Euclidean setting.