Abstract
We prove that the critical value β c of a ferromagnetic Potts model is astrictly decreasing function of the strengths of interaction of the process. This is achieved in the (more) general context of the random-cluster representation of Fortuin and Kasteleyn, by deriving and utilizing a formula which generalizes the technique known in percolation theory as Russo's formula. As a byproduct of the method, we present a general argument for showing that, at any given point on the critical surface of a multiparameter process, the values of a certain critical exponent do not depend on the direction of approach of that point. Our results apply to all random-cluster processes satisfying the FKG inequality.
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Communicated by M. Aizenman
G.R.G. acknowledges support from Cornell University, and also partial support by the U.S. Army Research Office through the Mathematical Sciences Institute of Cornell University. H.K. was supported in part by the N.S.F. through a grant to Cornell University
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Bezuidenhout, C.E., Grimmett, G.R. & Kesten, H. Strict inequality for critical values of Potts models and random-cluster processes. Commun.Math. Phys. 158, 1–16 (1993). https://doi.org/10.1007/BF02097229
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DOI: https://doi.org/10.1007/BF02097229