On some moves on links and the Hopf crossing number

Abstract

We consider arrow diagrams of links in $S^3$ and define $k$-moves on such diagrams, for any $k\in \mathbb{N}$. We study the equivalence classes of links in $S^3$ up to $k$-moves. For $k=2$, we show that any two knots are equivalent, whereas it is not true for links. We show that the Jones polynomial at a $k$-th primitive root of unity is unchanged by a $k$-move, when $k$ is odd. It is multiplied by $-1$, when $k$ is even. It follows that, for any $k\ge 5$, there are infinitely many classes of knots modulo $k$-moves. We use these results to study the Hopf crossing number. In particular, we show that it is unbounded for some families of knots. We also interpret $k$-moves as some identifications between links in different lens spaces $L_{p,1}$.

arXiv comment15 pages, 10 figures