The reciprocal-specialization formula for q,t-Fuss-Catalan numbers

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Let WW be a well-generated complex reflection group of rank ℓ\ell, acting on C[V⊕V∗]\mathbb{C}[V\oplus V^*]. Let did_i and di∗d_i^* be the invariant and codegrees appearing in the source, let hh be the Coxeter number, and set

N=∑i(di−1),N∗=∑i(di∗+1).N=\sum_i(d_i-1),\qquad N^*=\sum_i(d_i^*+1).

Here NN is the number of reflections and N∗N^* is the number of reflecting hyperplanes. Reciprocal-specialization conjecture.

qmNCat⁡(m)(W;q,q−1)=qmN∗Cat⁡(m)(W;q−1,q)=∏i=1ℓ[di+mh]q[di]q.q^{mN}\operatorname{Cat}^{(m)}(W;q,q^{-1})=q^{mN^*}\operatorname{Cat}^{(m)}(W;q^{-1},q)=\prod_{i=1}^{\ell}\frac{[d_i+mh]_q}{[d_i]_q}.

This is intended to generalize the corresponding type AA formula and is stronger than the dimension conjecture; the source gives no resolution.

References

Primary source

Christian Stump, “q,t-Fuss-Catalan numbers for finite reflection groups”, arXiv:0901.1574 (2009).

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