The inversion-major-index equidistribution conjecture for reduced words of the longest permutation

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Let w0(n)w_0^{(n)} be the longest permutation in athcalSnathcalS_n and let Red⁡(w0(n))\operatorname{Red}(w_0^{(n)}) denote its reduced words. For a reduced word ρ\rho, define its inversion statistic inv⁡(ρ)\operatorname{inv}(\rho) as in the paper, and define the major index by

maj⁡(ρ)=∑i: ρi+1>ρii.\operatorname{maj}(\rho)=\sum_{i:\,\rho_{i+1}>\rho_i}i.

Inversion-major-index equidistribution conjecture. For n≥1n\geq 1,

∑ρ∈Red⁡(w0(n))qinv⁡(ρ)=[(n2)]q![1]qn−1[3]qn−2[5]qn−3⋯[2n−3]q1=∑ρ∈Red⁡(w0(n))qmaj⁡(ρ)−(n3).\sum_{\rho\in\operatorname{Red}(w_0^{(n)})}q^{\operatorname{inv}(\rho)}=\frac{\left[\binom{n}{2}\right]_q!}{[1]_q^{n-1}[3]_q^{n-2}[5]_q^{n-3}\cdots[2n-3]_q^1}=\sum_{\rho\in\operatorname{Red}(w_0^{(n)})}q^{\operatorname{maj}(\rho)-\binom{n}{3}}.

The displayed identity is a proposed qq-analogue of the known major-index formula for reduced words of the longest permutation, relating the newly defined inversion statistic to the major index. The supplied text does not state whether this conjecture has been proved or disproved.

References

Primary source

Sami Assaf, “An inversion metric for reduced words”, arXiv:1808.01281 (2018).

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