A Non-Abelian Generalization of the Alexander Polynomial from Quantum $\mathfrak{sl}_3$ (2008.06983v3)

Abstract: Murakami and Ohtsuki have shown that the Alexander polynomial is an $R$-matrix invariant associated with representations $V(t)$ of unrolled restricted quantum $\mathfrak{sl}2$ at a fourth root of unity. In this context, the highest weight $t\in\mathbb{C}^\times$ of the representation determines the polynomial variable. For any semisimple Lie algebra $\mathfrak{g}$ of rank $n$, we extend their construction to a link invariant $\Delta{\mathfrak{g}}$, which takes values in $n$-variable Laurent polynomials. The focus of this paper is the case $\mathfrak{g}=\mathfrak{sl}3$. For any knot $K$, evaluating $\Delta{\mathfrak{sl}3}$ at ${t_1=1}$, ${t_2=1}$, or ${t_2= it_1^{-1}}$ recovers the Alexander polynomial of $K$. This is not obvious from an examination of the $R$-matrix, as the $R$-matrix evaluated at these parameters does not satisfy the Alexander-Conway skein relation. We tabulate $\Delta{\mathfrak{sl}_3}$ for all knots up to seven crossings along with various other examples. In particular, it distinguishes the Kinoshita-Terasaka knot and Conway knot mutant pair and is nontrivial on the Whitehead double of the trefoil.