The two upper critical dimensions of the Ising and Potts models
Kay Jörg Wiese, Jesper Lykke Jacobsen1
1CNRS-Laboratoire de Physique de
l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Universités, Université Paris-Diderot, Sorbonne Paris Cité
24 rue Lhomond, 75005 Paris, France
Abstract
We derive the exact actions of the $Q$-state Potts model valid on any graph, first for the spin degrees of freedom, and second for the Fortuin-Kasteleyn clusters. In both cases the field is a traceless $Q$-component scalar field $\Phi^\alpha$.
For the Ising model ($Q=2$), the field theory for the spins has upper critical dimension $d_{\rm c}^{\rm spin}=4$, whereas for the clusters it has $d_{\rm c}^{\rm cluster}=6$.
As a consequence, the probability for three points to be in the same cluster is not given by mean-field theory theory for $d$ within $4 < d < 6$. We estimate the associated universal structure constant as $C=\sqrt{6-d}+ {\cal O}(6-d)^{3/2}$. This shows that some observables in the Ising model have an upper critical dimension of 4, while others have an upper critical dimension of $6$.
Combining perturbative results from the $\epsilon=6-d$ expansion with a non-perturbative treatment close to dimension $d=4$ allows us to locate the shape of the critical domain of the Potts model in the whole $(Q,d)$ plane.
arXiv:2311.01529 [pdf]
Copyright (C)
by Kay Wiese. Last edited November 6, 2023.