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On the symmetric braid index of ribbon knots

Published online by Cambridge University Press:  05 August 2025

VITALIJS BREJEVS  and
FERIDE CEREN KÖSE
VITALIJS BREJEVS
Affiliation:
Riga, Latvia e-mail: brejka@gmail.com
FERIDE CEREN KÖSE
Affiliation:
Department of Mathematics, University of Georgia e-mail: fceren@uga.edu
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Abstract

We define the symmetric braid index $b_s(K)$ of a ribbon knot K to be the smallest index of a braid whose closure yields a symmetric union diagram of K, and derive a Khovanov-homological characterisation of knots with $b_s(K)$ at most three. As applications, we show that there exist knots whose symmetric braid index is strictly greater than the braid index, and deduce that every chiral slice knot with determinant one has braid index at least four. We also calculate bounds for $b_s(K)$ for prime ribbon knots with at most 11 crossings.

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Type
Research Article
Information
Mathematical Proceedings of the Cambridge Philosophical Society , First View , pp. 1 - 14
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of Cambridge Philosophical Society

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