The q-Kreweras cyclic sieving conjecture for principal-in-a-Levi nilpotent orbits

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Let WW be a Weyl group with Coxeter number hh, let m=sh+1m=sh+1, and let NC(s)(W)NC^{(s)}(W) denote the set of multichains w1≤⋯≤wsw_1\leq\cdots\leq w_s in the ss-divisible noncrossing partition poset. For each WW-orbit [X][X] of subsets XX of a Cartan subalgebra, let lX\mathfrak l_X be the corresponding Levi subalgebra and let \0X\0_X be the nilpotent orbit consisting of elements principal nilpotent in lX\mathfrak l_X. The cyclic group Z/shZ\mathbb Z/sh\mathbb Z acts on NC(s)(W)NC^{(s)}(W), and ωd\omega_d denotes a primitive ddth root of unity. The q-Kreweras cyclic sieving conjecture. For each WW-orbit [X][X], Krew(Φ,\0X,m;q=ωd)\mathrm{Krew}(\Phi,\0_X,m;q=\omega_d) counts the elements w1≤⋯≤ws∈NC(s)(W)w_1\leq\cdots\leq w_s\in NC^{(s)}(W) that are fixed by an element of order dd in the Z/shZ\mathbb Z/sh\mathbb Z-action and satisfy Vw1∈[X]V^{w_1}\in[X]. This would provide the q-analogue of the Kreweras numbers and generalize the cyclic sieving result for Fuss–Catalan numbers.

References

Primary source

Victor Reiner and Eric Sommers, “Weyl group q-Kreweras numbers and cyclic sieving”, arXiv:1605.09172 (2016).

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