Lewis's Hurwitz-orbit classification conjecture for finite Coxeter groups

Let WW be a finite Coxeter group and let gWg\in W be an arbitrary element. A reflection factorization of gg is a tuple of reflections whose product is gg, and the Hurwitz action acts on such factorizations by the standard Hurwitz moves. For a factorization (g1,,gk)(g_1,\ldots,g_k), let

H=g1,,gkWH=\langle g_1,\ldots,g_k\rangle\leq W

and consider the multiset of HH-conjugacy classes of its factors.

Lewis's conjecture. Two reflection factorizations of gg belong to the same Hurwitz orbit if and only if they generate the same subgroup HWH\leq W and have the same multiset of HH-conjugacy classes.

The product, generated subgroup, and multiset of conjugacy classes are evident invariants of the Hurwitz action. The conjecture was originally posed for complex reflection groups, but the source notes counterexamples for minimum-length reflection factorizations in two exceptional complex reflection groups; the finite Coxeter-group formulation is the claim considered here.

Sources & referencesView supporting material

Primary source

Theo Douvropoulos and Joel Brewster Lewis, “In which it is proven that, for each parabolic quasi-Coxeter element in a finite real reflection group, the orbits of the Hurwitz action on its reflection factorizations are distinguished by the two obvious invariants”, arXiv:2209.00774 (2023).

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