Conjectural braid-index formulas for exceptional Type 3 pretzel links

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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

L∈P3(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

L∈P3(1;−3∣2α1,…,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 αj≥2\alpha_j\ge 2 for 1≤j≤κ+−21\le j\le \kappa^+-2. For negative parameters, consider

L∈P3(ν1+1;−ν1∣0;−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

L∈P3(3;−1∣0;−2β1,…,−2βκ−−2,−4,−2;0)\mathcal{L}\in P_3(3;-1\vert 0;-2\beta_1,\ldots,-2\beta_{\kappa^--2},-4,-2;0)

with βi≥2\beta_i\ge 2 for 1≤i≤κ−−21\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.

References

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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