Self-linking number
In knot theory, the self-linking number is an invariant of framed knots. It is related to the linking number of curves.
A framing of a knot is a choice of a non-zero non-tangent vector at each point of the knot. More precisely, a framing is a choice of a non-zero section in the normal bundle of the knot, i.e. a (non-zero) normal vector field. Given a framed knot C, the self-linking number is defined to be the linking number of C with a new curve obtained by pushing points of C along the framing vectors.
Given a Seifert surface for a knot, the associated Seifert framing is obtained by taking a tangent vector to the surface pointing inwards and perpendicular to the knot. The self-linking number obtained from a Seifert framing is always zero.[1]
The blackboard framing of a knot is the framing where each of the vectors points in the vertical (z) direction. The self-linking number obtained from the blackboard framing is called the Kauffman self-linking number of the knot. This is not a knot invariant because it is only well-defined up to regular isotopy.
References
- ↑ Sumners, De Witt L.; Cruz-White, Irma I.; Ricca, Renzo L. (2021). "Zero helicity of Seifert framed defects". J. Phys. A 54 (29): 295203. doi:10.1088/1751-8121/abf45c. Bibcode: 2021JPhA...54C5203S.
- Chernov, Vladimir (2005), "Framed knots in 3-manifolds and affine self-linking numbers", Journal of Knot Theory and its Ramifications 14 (6): 791–818, doi:10.1142/S0218216505004056.
- Moskovich, Daniel (2004), "Framing and the self-linking integral", Far East Journal of Mathematical Sciences 14 (2): 165–183, Bibcode: 2002math.....11223M
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