Finitary codings for gradient models and a new graphical representation for the six-vertex model

TL;DR

This paper investigates the finitary coding properties of gradient models like the Ising, Potts, and six-vertex models, introducing a new graphical representation and demonstrating conditions under which these models or their derivatives are finitary factors of i.i.d. processes.

Contribution

It establishes that the gradient of the Ising and Potts models are finitary factors of i.i.d., introduces a novel graphical representation for the six-vertex model, and explores the finitary properties of its Laplacian.

Findings

Gradient of Ising model is a finitary factor at all temperatures.

New graphical representation for the six-vertex model with parameter c ≈ 6.4.

Gradient of the height function in the six-vertex model is not finitary, but its Laplacian is.

Abstract

It is known that the Ising model on $\mathbb {Z}^d$ at a given temperature is a finitary factor of an i.i.d. process if and only if the temperature is at least the critical temperature. Below the critical temperature, the plus and minus states of the Ising model are distinct and differ from one another by a global flip of the spins. We show that it is only this global information which poses an obstruction for being finitary by showing that the gradient of the Ising model is a finitary factor of i.i.d. at all temperatures. As a consequence, we deduce a volume-order large deviation estimate for the energy. A similar result is shown for the Potts model. A result in the same spirit is also shown for the six-vertex model, which is itself the gradient of a height function, with parameter $c \gtrapprox 6.4$. We show that the gradient of the height function is not a finitary factor of an i.i.d. process, but that its "Laplacian" is. For this, we introduce a coupling between the six-vertex model with $c\ge 2$ and a new graphical representation of it, reminiscent of the Edwards--Sokal coupling between the Potts and random-cluster models. We believe that this graphical representation may be of independent interest and could serve as a tool in further understanding of the six-vertex model. To provide further support for the ubiquity of this type of phenomenon, we also prove an analogous result for the so-called beach model. The tools and techniques used in this paper are probabilistic in nature. The heart of the argument is to devise a suitable tree structure on the clusters of the underlying percolation process (associated to the graphical representation of the given model), which can be revealed piece-by-piece via exploration.