Singularization of knots and closed braids

Thomas Fiedler

Published 2014-05-21, updated 2015-07-05Version 3

We construct the first combinatorial 1-cocycle with values in the $ \mathbb{Z} [x,x^{-1}]$-module of isotopy classes of singular long knots in 3-space with a signed planar double point, and which represents a non trivial cohomology class in the topological moduli space of long knots. It can be interpreted as an invariant with values in a $ \mathbb{Z} [x,x^{-1}]$-module generated by 3-manifolds for each element of infinite order of the mapping class group of the complement of a satellite knot in $S^3$. The 1-cocycle seems to be trivial on all loops for long knots which are not satellites but it is already non trivial on the Fox-Hatcher loop of any composite knot, on the loop which consists of {\em dragging} a trefoil through another trefoil and on the {\em scan-arc} for the 2-cable of the trefoil. The {\em canonical resolution} of the value of the 1-cocycle for dragging a knot through another knot leads to a symmetric bilinear form on the free $ \mathbb{Z} [x,x^{-1}]$-module of all unframed oriented knot types into itself. We conjecture that its radical contains only the trivial knot. Evaluating e.g. the Kauffman-Vogel HOMFLYPT polynomial for singular knots on the value of the 1-cocycle applied to the associated quadratic form, leads to a couple of new 3-variable knot polynomials. We construct also the first non trivial 1-cocycle for those closed positive 4-braids which contain a half-twist. It takes its values in a symmetric power of the $ \mathbb{Z}$-module of isotopy classes of closed positive 4-braids with a double point.