S-Equivalence of Band-Twisted Genus One Knots

Abstract

We add twists to a band of a genus-one Seifert surface, producing a knot $K(\ell ,0)$. We prove $K$ and $K(\ell ,0)$ have $S$-equivalent Seifert matrices if and only if the $(2,2)$-entry of the Seifert matrix vanishes and the sum of off-diagonal entries divides $\ell$. The necessity follows from the Alexander polynomial and a norm argument proving triviality of the $S$-equivalence subgroup ${\mathcal{S}}^{+}$ in the class group of binary quadratic forms (Aka--Feller--Miller--Wieser); sufficiency is an explicit ${\Lambda }_1$-operation. The Jones polynomial distinguishes the knots when $V(K)\ne 1$, yielding infinite families of $S$-equivalent but inequivalent genus-one knots, illustrated by $9_{46}$. Also in this paper, we provide a partial answer for Problem~1.6 in Kirby's problem list (K3) and Problem~7.7 of Aka--Feller--Miller--Wieser.