Conjectural braid-index formulas for exceptional Type 3 pretzel links

Let L\mathcal{L} be a Type 3 pretzel link, and let b(L)\textbf{b}(\mathcal{L}) denote its braid index. For positive parameters, consider

LP3(μ1;(μ1+1)2α1,,2ακ+;0)\mathcal{L}\in P_3(\mu_1;-(\mu_1+1)\vert 2\alpha_1,\ldots,2\alpha_{\kappa^+};0)

with μ1>1\mu_1>1 and 1<min{αj}μ11<\min\{\alpha_j\}\le \mu_1, or

LP3(1;32α1,,2ακ+2,4,2;0)\mathcal{L}\in P_3(1;-3\vert 2\alpha_1,\ldots,2\alpha_{\kappa^+-2},4,2;0)

with αj2\alpha_j\ge 2 for 1jκ+21\le j\le \kappa^+-2. For negative parameters, consider

LP3(ν1+1;ν10;2β1,,2βκ)\mathcal{L}\in P_3(\nu_1+1;-\nu_1\vert 0;-2\beta_1,\ldots,-2\beta_{\kappa^-})

with ν1>1\nu_1>1 and 1<min{βi}ν11<\min\{\beta_i\}\le \nu_1, or

LP3(3;10;2β1,,2βκ2,4,2;0)\mathcal{L}\in P_3(3;-1\vert 0;-2\beta_1,\ldots,-2\beta_{\kappa^--2},-4,-2;0)

with βi2\beta_i\ge 2 for 1iκ21\le i\le \kappa^--2.

Conjectural Type 3 braid-index formulas. In the first positive case, b(L)=2+αj\textbf{b}(\mathcal{L})=2+\sum\alpha_j; in the second positive case, b(L)=1+αj\textbf{b}(\mathcal{L})=1+\sum\alpha_j. In the first negative case, b(L)=2+βi\textbf{b}(\mathcal{L})=2+\sum\beta_i; and in the second negative case, b(L)=1+βi\textbf{b}(\mathcal{L})=1+\sum\beta_i.

These formulas are proposed as the concluding conjecture of the authors' study of Type 3 pretzel links, based on computational results and the proof of one related case. The stated braid indices are not established in the source, so the conjecture remains open.

Sources & referencesView supporting material

Primary source

Yuanan Diao, Claus Ernst and Gabor Hetyei, “The Braid Indices of Pretzel Links: A Comprehensive Study, Part II”, arXiv:2407.00238 (2024).

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