Minimal coloring number on minimal diagrams for $\mathbb{Z}$-colorable links

Abstract

It was shown that any $\mathbb{Z}$-colorable link has a diagram which admits a non-trivial $\mathbb{Z}$-coloring with at most four colors. In this paper, we consider minimal numbers of colors for non-trivial $\mathbb{Z}$-colorings on minimal diagrams of $\mathbb{Z}$-colorable links. We show, for any positive integer $N$, there exists a minimal diagram of a $\mathbb{Z}$-colorable link such that any $\mathbb{Z}$-coloring on the diagram has at least $N$ colors. On the other hand, it is shown that certain $\mathbb{Z}$-colorable torus links have minimal diagrams admitting $\mathbb{Z}$-colorings with only four colors.

7 pages, 9 figures; v2. Theorem 2.2 is revised. To appear in Proceedings of the Institute of Natural Sciences, Nihon University