Polynomial invariants of singular knots and links

We generalize the notion of the quandle polynomial to the case of singquandles. We show that the singquandle polynomial is an invariant of finite singquandles. We also construct a singular link invariant from the singquandle polynomial and show that this new singular link invariant generalizes the singquandle counting invariant. In particular, using the new polynomial invariant, we can distinguish singular links with the same singquandle counting invariant.

Writhe-like invariants of alternating links

It is known that the writhe calculated from any reduced alternating link diagram of the same (alternating) link has the same value. That is, it is a link invariant if we restrict ourselves to reduced alternating link diagrams. This is due to the fact that reduced alternating link diagrams of the same link are obtainable from each other via flypes and flypes do not change writhe. In this paper, we introduce several quantities that are derived from Seifert graphs of reduced alternating link diagrams. We prove that they are “writhe-like” invariants, namely they are not general link invariants, but are invariants when restricted to reduced alternating link diagrams. The determination of these invariants are elementary and non-recursive so they are easy to calculate. We demonstrate that many different alternating links can be easily distinguished by these new invariants, even for large, complicated knots for which other invariants such as the Jones polynomial are hard to compute. As an application, we also derive an if and only if condition for a strongly invertible rational link.

Are Maxwell knots integrable?

We review properties of the null-field solutions of source-free Maxwell equations. We focus on the electric and magnetic field lines, especially on limit cycles, which actually can be knotted and/or linked at every given moment. We analyse the fact that the Poynting vector induces self-consistent time evolution of these lines and demonstrate that the Abelian link invariant is integral of motion. We also consider particular examples of the field lines for the particular family of finite energy source-free “knot” solutions, attempting to understand when the field lines are closed – and can be discussed in terms of knots and links. Based on computer simulations we conjecture that Ranada’s solution, where every pair of lines forms a Hopf link, is rather exceptional. In general, only particular lines (a set of measure zero) are limit cycles and represent closed lines forming knots/links, while all the rest are twisting around them and remain unclosed. Still, conservation laws of Poynting evolution and associated integrable structure should persist.

A generalized skein relation for Khovanov homology and a categorification of the θ-invariant

The Jones polynomial is a famous link invariant that can be defined diagrammatically via a skein relation. Khovanov homology is a richer link invariant that categorifies the Jones polynomial. Using spectral sequences, we obtain a skein-type relation satisfied by the Khovanov homology. Thanks to this relation, we are able to generalize the Khovanov homology in order to obtain a categorification of the θ-invariant, which is itself a generalization of the Jones polynomial.

A simple algorithm to compute link polynomials defined by using skein relations

We give a simple and practical algorithm to compute the link polynomials, which are defined according to the skein relations. Our method is based on a new total order on the set of all braid representatives. As by-product a new complete link invariant are obtained.

An invariant of graph-links valued in graphs and an almost classification of graph-links

In [V. O. Manturov, An almost classification of free knots, Dokl. Math. 88(2) (2013) 556–558.] the second author constructed an invariant which in some sense generalizes the quantum [Formula: see text] link invariant of Kuperberg to the case of free links. In this paper, we generalize this construction to free graph-links. As a result, we obtain an invariant of free graph-links with values in linear combinations of graphs. The main property of this invariant is that under certain conditions on the representative of the free graph-link, we can recover this representative from the value invariant on it. In addition, this invariant allows one to partially classify free graph-links.

A description of Rasmussen’s invariant from the divisibility of Lee’s canonical class

We give a description of Rasmussen’s [Formula: see text]-invariant from the divisibility of Lee’s canonical class. More precisely, given any link diagram [Formula: see text], for any choice of an integral domain [Formula: see text] and a non-zero, non-invertible element [Formula: see text], we define the [Formula: see text]-divisibility [Formula: see text] of Lee’s canonical class of [Formula: see text], and prove that a combination of [Formula: see text] and some elementary properties of [Formula: see text] yields a link invariant [Formula: see text]. Each [Formula: see text] possesses properties similar to [Formula: see text], which in particular reproves the Milnor conjecture. If we restrict to knots and take [Formula: see text], then our invariant coincides with [Formula: see text].

Integral metaplectic modular categories

A braided fusion category is said to have Property F if the associated braid group representations factor through a finite group. We verify integral metaplectic modular categories have property F by showing these categories are group-theoretical. For the special case of integral categories [Formula: see text] with the fusion rules of [Formula: see text] we determine the finite group [Formula: see text] for which [Formula: see text] is braided equivalent to [Formula: see text]. In addition, we determine the associated classical link invariant, an evaluation of the 2-variable Kauffman polynomial at a point.

A note on the S-dual basis in the free fermion system

The free fermion system is the simplest quantum field theory which has the symmetry of the Ding–Iohara–Miki algebra (DIM). DIM has S-duality symmetry, known as Miki automorphism, which defines the transformation of generators. We introduce the second set of the fermionic basis (S-dual basis) which implements the duality transformation. It may be interpreted as the Fourier dual of the standard basis, and the inner product between the standard and the S-dual is proportional to the Hopf link invariant. We also rewrite the general topological vertex in the form of an Awata–Feigin–Shiraishi intertwiner and show that it becomes more symmetric for the duality transformation.

Multivariate Alexander quandles, III. Sublinks

If [Formula: see text] is a classical link then the multivariate Alexander quandle, [Formula: see text], is a substructure of the multivariate Alexander module, [Formula: see text]. In the first paper of this series, we showed that if two links [Formula: see text] and [Formula: see text] have [Formula: see text], then after an appropriate re-indexing of the components of [Formula: see text] and [Formula: see text], there will be a module isomorphism [Formula: see text] of a particular type, which we call a “Crowell equivalence.” In this paper, we show that [Formula: see text] (up to quandle isomorphism) is a strictly stronger link invariant than [Formula: see text] (up to re-indexing and Crowell equivalence). This result follows from the fact that [Formula: see text] determines the [Formula: see text] quandles of all the sublinks of [Formula: see text], up to quandle isomorphisms.