Normalizer and conjugator description for standard parabolic subgroups of Artin groups

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Let AA be an Artin group such that every irreducible AZA_Z with ∣Z∣>2|Z|>2 is not of spherical type. For X⊆SX\subseteq S, write

X⊥={y∈S∖X∣xy=yx, ∀x∈X}.X^\bot=\{y\in S\setminus X\mid xy=yx,\ \forall x\in X\}.

If AXA_X has no cyclic irreducible component ⟨x⟩\langle x\rangle with x∈Xx\in X, then its normalizer is

N(AX)=AX×AX⊥.N(A_X)=A_X\times A_{X^\bot}.

Otherwise, the elements that conjugate XX to YY are given by

Conj(X,Y)=(Ribb(X,Y)⋅AX)⋅AX⊥.\mathrm{Conj}(X,Y)=(\mathrm{Ribb}(X,Y)\cdot A_X)\cdot A_{X^\bot}.

This describes normalizers and conjugators of standard parabolic subgroups under the hypothesis that irreducible components with more than two generators are not spherical. The source presents the statement as an auxiliary result adapted from Godelle's conjecture, but provides no resolution status for the underlying claim.

References

Primary source

Bruno Aaron Cisneros de la Cruz, María Cumplido and Islam Foniqi, “On Artin groups admitting retractions to parabolic subgroups”, arXiv:2408.12291 (2024).

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