Closed 3-braids are nearly fibred

Mutual braiding and the band presentation of braid groups

This paper is concerned with detecting when a closed braid and its axis are 'mutually braided' in the sense of Rudolph. It deals with closed braids which are fibred links, the simplest case being closed braids which present the unknot. The geometric condition for mutual braiding refers to the existence of a close control on the way in which the whole family of fibre surfaces meet the family of discs spanning the braid axis. We show how such a braid can be presented naturally as a word in the `band generators' of the braid group discussed by Birman, Ko and Lee in their recent account of the ban…

Two strand twisting

We prove that fibred knots cannot be untied with $\bar{t}_{2k}$-moves, for all $k \geq 2$. More generally, we give an upper bound on the number of two strand twist operations that allow to untie a knot with non-trivial HOMFLY polynomial, in terms of the minimal crossing number, and the braid index. As a by-product, we prove that the braid index of a two-bridge knot cannot be lowered by applying $t_{2k}$-moves, for all but finitely many $k \in \mathbb{N}$.

Floer同调、扣环辫与检测结果

Floer homology, clasp-braids and detection results

本文拓展Martin的辫轴检测结果，基于链环Floer同调给出近辫状链环的拓扑刻画，受近纤维化纽结研究启发，得到Khovanov同调等的多类检测应用。