For a graph $G=(V,E)$, $k\in \mathbb{N}$, and a complex number $w$ the partition function of the univariate Potts model is defined as \[ {\bf Z}(G;k,w):=\sum_{\phi:V\to [k]}\prod_{\substack{uv\in E \\ \phi(u)=\phi(v)}}w, \] where $[k]:=\{1,\ldots,k\}$. In this paper we give zero-free regions for the partition function of the anti-ferromagnetic Potts model on bounded degree graphs. In particular we show that for any $\Delta\in \mathbb{N}$ and any $k\geq e\Delta+1$, there exists an open set $U$ in the complex plane that contains the interval $[0,1)$ such that ${\bf Z}(G;k,w)\neq 0$ for any $w\in U$ and any graph $G$ of maximum degree at most $\Delta$. (Here $e$ denotes the base of the natural logarithm.) For small values of $\Delta$ we are able to give better results. As an application of our results we obtain improved bounds on $k$ for the existence of deterministic approximation algorithms for counting the number of proper $k$-colourings of graphs of small maximum degree.
翻译:$G = (V, E) $, $k\ in\ mathbb{N) $, 以及一个复杂数字 $。 在本文中, 我们给无价区域, 用于在约束度图上 的反热磁器模型的分区功能 。 特别是, 我们显示, 对于任何$\\ Delta\\ in\ mathb{N} 美元和任何$k\ geq e\\ Delta+1 美元, 复杂平面上有一个开放的 $U, 包含 $[ 0. 1,\\\\ ldots, k$ 。 在固定度图中, 我们给反热磁器的模型的分区函数分配功能, 零美元 。 对于任何最小值的 美元, 最大值为 美元 美元 的 。 对于任何最小值的硬值, 我们的硬值为 。