Finite-type invariants of w-knotted objects, I: w-knots and the Alexander polynomial

Bar-Natan, Dror¹ ; Dancso, Zsuzsanna²

¹Department of Mathematics, University of Toronto, Toronto ON M5S 2E4, Canada
²Mathematical Sciences Institute, Australian National University, John Dedman Building 27, Union Ln, Canberra ACT 2601, Australia

Algebraic and Geometric Topology, Tome 16 (2016) no. 2, pp. 1063-1133

Résumé

This is the first in a series of papers studying w-knots, and more generally, w-knotted objects (w-braids, w-tangles, etc). These are classes of knotted objects which are wider, but weaker than their “usual” counterparts.

The group of w-braids was studied (under the name “welded braids”) by Fenn, Rimanyi and Rourke and was shown to be isomorphic to the McCool group of “basis-conjugating” automorphisms of a free group Fn: the smallest subgroup of Aut(Fn) that contains both braids and permutations. Brendle and Hatcher, in work that traces back to Goldsmith, have shown this group to be a group of movies of flying rings in ℝ3. Satoh studied several classes of w-knotted objects (under the name “weakly-virtual”) and has shown them to be closely related to certain classes of knotted surfaces in ℝ4. So w-knotted objects are algebraically and topologically  interesting.

Here we study finite-type invariants of w-braids and w-knots. Following Berceanu and Papadima, we construct homomorphic universal finite-type invariants of w-braids. The universal finite-type invariant of w-knots is essentially the Alexander polynomial.

Much as the spaces A of chord diagrams for ordinary knotted objects are related to metrized Lie algebras, the spaces Aw of “arrow diagrams” for w-knotted objects are related to not-necessarily-metrized Lie algebras. Many questions concerning w-knotted objects turn out to be equivalent to questions about Lie algebras. Later in this paper series we re-interpret the work of Alekseev and Torossian on Drinfel’d associators and the Kashiwara–Vergne problem as a study of w-knotted trivalent graphs.

Détail

DOI : 10.2140/agt.2016.16.1063

Classification : 57M25, 57Q45
Keywords: virtual knots, w-braids, w-knots, w-tangles, welded knots, knotted graphs, finite-type invariants, Alexander polynomial, Kashiwara–Vergne, associators, free Lie algebras

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