English

The Chromatic Number of $\mathbb{R}^{n}$ with Multiple Forbidden Distances

Combinatorics 2023-03-13 v2

Abstract

Let AR>0A\subset\mathbb{R}_{>0} be a finite set of distances, and let GA(Rn)G_{A}(\mathbb{R}^{n}) be the graph with vertex set Rn\mathbb{R}^{n} and edge set {(x,y)Rn: xy2A}\{(x,y)\in\mathbb{R}^{n}:\ \|x-y\|_{2}\in A\}, and let χ(Rn,A)=χ(GA(Rn))\chi(\mathbb{R}^{n},A)=\chi\left(G_{A}(\mathbb{R}^{n})\right). Erd\H{o}s asked about the growth rate of the mm-distance chromatic number χˉ(Rn;m)=maxA=mχ(Rn,A). \bar{\chi}(\mathbb{R}^{n};m)=\max_{|A|=m}\chi(\mathbb{R}^{n},A). We improve the best existing lower bound for χˉ(Rn;m)\bar{\chi}(\mathbb{R}^{n};m), and show that χˉ(Rn;m)(Γχm+1+o(1))n \bar{\chi}(\mathbb{R}^{n};m)\geq\left(\Gamma_{\chi}\sqrt{m+1}+o(1)\right)^{n} where Γχ=0.79983\Gamma_{\chi}=0.79983\dots is an explicit constant. Our full result is more general, and applies to cliques in this graph. Let χk(G)\chi_{k}(G) denote the minimum number of colors needed to color GG so that no color contains a (k+1)(k+1)-clique, and let χˉk(Rn;m)\bar{\chi}_{k}(\mathbb{R}^{n};m) denote the largest value this takes for any distance set of size mm . Using the Partition Rank Method, we show that χˉk(Rn;m)>(Γχm+1k+o(1))n. \bar{\chi}_{k}(\mathbb{R}^{n};m)>\left(\Gamma_{\chi}\sqrt{\frac{m+1}{k}}+o(1)\right)^{n}.

Keywords

Cite

@article{arxiv.2205.12312,
  title  = {The Chromatic Number of $\mathbb{R}^{n}$ with Multiple Forbidden Distances},
  author = {Eric Naslund},
  journal= {arXiv preprint arXiv:2205.12312},
  year   = {2023}
}

Comments

21 pages. Removed section 2. To appear in Mathematika