# On zero-free regions for the anti-ferromagnetic Potts model on bounded-degree graphs

## TL;DR

This paper establishes zero-free regions for the anti-ferromagnetic Potts model's partition function on bounded degree graphs, leading to improved bounds for approximation algorithms in graph coloring problems.

## Contribution

It provides new zero-free regions for the Potts model on bounded degree graphs, enhancing understanding of phase transitions and algorithmic applications.

## Key findings

- Zero-free regions for the partition function are identified for graphs with bounded degree.
- For large enough k, there exists an open set in the complex plane where the partition function does not vanish.
- Results lead to improved bounds on k for deterministic approximation algorithms for graph colorings.

## Abstract

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.

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Source: https://tomesphere.com/paper/1812.07532