Fibered knot

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Fibered knot
Figure-eight knot is fibered.

In knot theory, a branch of mathematics, a knot or link K {\displaystyle K} {\displaystyle K}
in the 3-dimensional sphere S 3 {\displaystyle S^{3}} {\displaystyle S^{3}} is called fibered or fibred (sometimes Neuwirth knot in older texts, after Lee Neuwirth) if there is a 1-parameter family F t {\displaystyle F_{t}} {\displaystyle F_{t}} of Seifert surfaces for K {\displaystyle K} {\displaystyle K}, where the parameter t {\displaystyle t} {\displaystyle t} runs through the points of the unit circle S 1 {\displaystyle S^{1}} {\displaystyle S^{1}}, such that if s {\displaystyle s} {\displaystyle s} is not equal to t {\displaystyle t} {\displaystyle t}
then the intersection of F s {\displaystyle F_{s}} {\displaystyle F_{s}} and F t {\displaystyle F_{t}} {\displaystyle F_{t}} is exactly K {\displaystyle K} {\displaystyle K}.

Examples

Knots that are fibered

For example:

Knots that are not fibered

Fibered knot
The stevedore knot is not fibered

The Alexander polynomial of a fibered knot is monic, i.e. the coefficients of the highest and lowest powers of t are plus or minus 1. Examples of knots with nonmonic Alexander polynomials abound, for example the twist knots have Alexander polynomials q t ( 2 q + 1 ) + q t 1 {\displaystyle qt-(2q+1)+qt^{-1}} {\displaystyle qt-(2q+1)+qt^{-1}}, where q is the number of half-twists.[1] In particular the stevedore knot is not fibered.

Related constructions

Fibered knots and links arise naturally, but not exclusively, in complex algebraic geometry. For instance, each singular point of a complex plane curve can be described
topologically as the cone on a fibered knot or link called the link of the singularity. The trefoil knot is the link of the cusp singularity z 2 + w 3 {\displaystyle z^{2}+w^{3}} {\displaystyle z^{2}+w^{3}}; the Hopf link (oriented correctly) is the link of the node singularity z 2 + w 2 {\displaystyle z^{2}+w^{2}} {\displaystyle z^{2}+w^{2}}. In these cases, the family of Seifert surfaces is an aspect of the Milnor fibration of the singularity.

A knot is fibered if and only if it is the binding of some open book decomposition of S 3 {\displaystyle S^{3}} {\displaystyle S^{3}}.

See also

References

  1. Fintushel, Ronald; Stern, Ronald J. (1998). “Knots, Links, and 4-Manifolds”. Inventiones Mathematicae. 134 (2): 363–400. arXiv:dg-ga/9612014. doi:10.1007/s002220050268. MR 1650308.

External links


This article is adapted from “Fibered knot” on Wikipedia, written by its contributors, and used under CC BY-SA 4.0. Text on this page is available under the same licence. Source snapshot: Wikipedia via Kiwix, 2026-07-20.