Physical Review Letters
Criterion for Distinguishing between Continuous and Discontinuous Transitions in Spin and Gauge Systems
Roberto Livi, Amos Maritan, Stefano Ruffo, Attilio L. Stella
Abstract
A conjecture, based on a comparison of different mean-field-like approximations, is proposed for determining the first- or second-order character of phase transitions. The $q$-state Potts model and several gauge theories [${Z}_{2}$, $\mathrm{U}(N)$, $\mathrm{SU}(N)$, SO(3)] on a lattice are considered. For ${Z}_{2}$ gauge theory, in particular, a critical dimensionality ${d}_{c}=3.66$ is predicted, whereas for the Potts model ${q}_{c}=2.75$ in $d=3$, ${q}_{c}=2.4$ in $d=4$, and ${q}_{c}\ensuremath{\propto}\mathrm{exp}[\frac{1}{(d\ensuremath{-}1)}]$ for $d\ensuremath{\rightarrow}1$ are obtained.