Iterated semidirect-product conjecture for braid-orbit permutation groups

Let G>IG>I be a finite group with Z(G)=IZ(G)=I. Let (C1,C2,C3,C4)(C_1,C_2,C_3,C_4) be a class vector of length 44 of GG, let ZΣ4i(C1,C2,C3,C4)Z\subseteq\Sigma^i_4(C_1,C_2,C_3,C_4) be a B4B_4-orbit with q=Z>0q=\lvert Z\rvert>0, and let ρ4:B4Sq\rho_4:B_4\to S_q be the induced permutation representation of the action of B4B_4 on ZZ.

Iterated semidirect-product conjecture.

ρ4(B4)Cnlkl((Cn2k2(Cn1k1Gm)))Sq,\rho_4(B_4)\cong C_{n_l}^{k_l}\rtimes(\cdots\rtimes(C_{n_2}^{k_2}\rtimes(C_{n_1}^{k_1}\rtimes G_m))\cdots)\leq S_q,

with Gm{Am,Sm}G_m\in\{A_m,S_m\}, qmn1nlq\mid m\cdot n_1\cdot\dots\cdot n_l, mqm\leq q, lN0l\in\mathbb{N}_0, n1,,nl{2,3}n_1,\dots,n_l\in\{2,3\}, k1,,klNk_1,\dots,k_l\in\mathbb{N}, and k1=m1k_1=m-1.

The conjecture proposes a restricted structure for the permutation groups arising from braid-group actions on these finite orbits. The supplied text motivates it through computations of examples, but provides no resolution.

Sources & referencesView supporting material

Primary source

Frank Häfner, “Braid orbits and the Mathieu group M_23 as Galois group”, arXiv:2202.08222 (2022).

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