A General Coupling for Ising Models and Beyond

Abstract: The couplings between the Ising model and its graphical representations, the random-cluster, random current and loop $\mathrm{O}(1)$ models, are put on common footing through a generalization of the Swendsen-Wang-Edwards-Sokal coupling. A new special case is that the single random current with parameter $2J$ on edges of agreement of XOR-Ising spins has the law of the double random current. The coupling also yields a general mechanism for constructing conditional Bernoulli percolation measures via uniform sampling, providing new perspectives on models such as the arboreal gas, random $d$-regular graphs, and self-avoiding walks. As an application of the coupling for the Loop-Cluster joint model, we prove that the regime of exponential decay of the $q$-state Potts model, the random-cluster representation, and its $q$-flow loop representation coincides on the torus, generalizing the Ising result. Finally, the Loop-Cluster coupling is generalized to lattice gauge theories.