Ising Model: Local Spin Correlations and Conformal Invariance

TL;DR

This paper rigorously analyzes the critical 2D Ising model on a lattice, establishing conformal covariance of local spin pattern probabilities and connecting lattice fields with conformal field theory through discrete complex analysis.

Contribution

It introduces explicit tools to translate lattice spin correlations into discrete complex analysis quantities, advancing the understanding of conformal invariance in the Ising model.

Findings

Proved conformal covariance of local spin pattern probabilities.

Established explicit formulas connecting lattice correlations to conformal fields.

Extended previous results to general local spin correlations.

Abstract

We study the 2-dimensional Ising model at critical temperature on a simply connected subset $\Omega_{\delta}$ of the square grid $\delta\mathbb{Z}^{2}$. The scaling limit of the critical Ising model is conjectured to be described by Conformal Field Theory; in particular, there is expected to be a precise correspondence between local lattice fields of the Ising model and the local fields of Conformal Field Theory. Towards the proof of this correspondence, we analyze arbitrary spin pattern probabilities (probabilities of finite spin configurations occurring at the origin), explicitly obtain their infinite-volume limits, and prove their conformal covariance at the first (non-trivial) order. We formulate these probabilities in terms of discrete fermionic observables, enabling the study of their scaling limits. This generalizes results of [Hon10,HoSm13] and [CHI15] to one-point functions of any local spin correlations. We introduce a collection of tools which allow one to exactly and explicitly translate any spin pattern probability (and hence any lattice local field correlation) in terms of discrete complex analysis quantities. The proof requires working with multipoint lattice spinors with monodromy (including construction of explicit formulae in the full plane), and refined analysis near their source points to prove convergence to the appropriate continuous conformally covariant functions.