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arXiv 1604.03033math.GT
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从Heegaard Floer同调中解开信息

Untwisting information from Heegaard Floer homology

Kenan Ince

AI总结:

本文研究解结数的推广——解扭数,证明Montesinos技巧不能用于阻碍低解扭数,但通过Heegaard Floer校正项给出解扭数为1的条件,并利用tau和s不变量区分不同p-解扭数。

摘要:

纽结的解结数(unknotting number)是将该纽结变为平凡纽结所需改变交叉点的最小数目。我们研究Mathieu-Domergue提出的解结数的一种推广,称之为解扭数(untwisting number)。p-解扭数是指(在纽结的所有图示上)在至多2p条线上施加完整扭转、其中一半线沿每个方向定向,从而将该纽结变为平凡纽结所需的最小扭转次数。在先前的工作中,我们证明了普通解结数与解扭数可以任意不同。在本文中,我们证明了一条常用于阻碍低解结数的途径,即Montesinos技巧,不能推广到解扭数。然而,我们采用一种不同的方法,对解扭数为1的纽结的分支双覆盖的Heegaard Floer校正项(correction terms)得到条件。这使我们能够阻碍若干10和11交叉点的纽结通过单个正或负扭转被解结。我们还使用Ozsváth-Szabó tau不变量和Rasmussen s不变量来区分某些p,q > 1时的p-解扭数与q-解扭数。

英文摘要:

The unknotting number of a knot is the minimum number of crossings one must change to turn that knot into the unknot. We work with a generalization of unknotting number due to Mathieu-Domergue, which we call the untwisting number. The p-untwisting number is the minimum number (over all diagrams of a knot) of full twists on at most 2p strands of a knot, with half of the strands oriented in each direction, necessary to transform that knot into the unknot. In previous work, we showed that the unknotting and untwisting numbers can be arbitrarily different. In this paper, we show that a common route for obstructing low unknotting number, the Montesinos trick, does not generalize to the untwisting number. However, we use a different approach to get conditions on the Heegaard Floer correction terms of the branched double cover of a knot with untwisting number one. This allows us to obstruct several 10 and 11-crossing knots from being unknotted by a single positive or negative twist. We also use the Ozsváth-Szabó tau invariant and the Rasmussen s invariant to differentiate between the p- and q-untwisting numbers for certain p,q > 1.

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