arXiv:2309.06489 · Physical review. E
q -state Potts model from the nonperturbative renormalization group
Carlos A. Sánchez-Villalobos, Bertrand Delamotte, Nicolás Wschebor
Abstract
We study the $q$-state Potts model for $q$ and the space dimension $d$ arbitrary real numbers using the derivative expansion of the nonperturbative renormalization group at its leading order, the local potential approximation (LPA and ${\mathrm{LPA}}^{\ensuremath{'}}$). We determine the curve ${q}_{c}(d)$ separating the first $[q>{q}_{c}(d)]$ and second $[q<{q}_{c}(d)]$ -order phase transition regions for $2.8<d\ensuremath{\le}4$. At small $\ensuremath{\epsilon}=4\ensuremath{-}d$ and $\ensuremath{\delta}=q\ensuremath{-}2$ the calculation is performed in a double expansion in these parameters, and we find ${q}_{c}(d)=2+a{\ensuremath{\epsilon}}^{2}$ with $a\ensuremath{\simeq}0.1$. For finite values of $\ensuremath{\epsilon}$ and $\ensuremath{\delta}$, we obtain this curve by integrating the LPA and ${\mathrm{LPA}}^{\ensuremath{'}}$ flow equations. We find that ${q}_{c}(d=3)=2.11(7)$, which confirms that the transition is of first order in $d=3$ for the three-state Potts model.