Equidistribution conjecture for ascents and descents of perfect matchings

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Let \PM2n\PM_{2n} denote the set of perfect matchings on [2n][2n], and let \Asc(m)\Asc(m) and \Des(m)\Des(m) be the ascent and descent sets of a matching m∈\PM2nm\in\PM_{2n}, defined by the relative order of si⋅ms_i\cdot m and mm in the matching order. For J⊆[2n−1]J\subseteq[2n-1], write

tJ:=∏j∈Jtj.\boldsymbol{t}^J:=\prod_{j\in J}t_j.

Equidistribution conjecture. For all n∈Nn\in\mathbb{N},

∑m∈\PM2nt\Asc(m)=∑m∈\PM2nt\Des(m).\sum_{m\in\PM_{2n}}\boldsymbol{t}^{\Asc(m)}=\sum_{m\in\PM_{2n}}\boldsymbol{t}^{\Des(m)}.

This asserts that the ascent and descent set statistics on perfect matchings are equidistributed. The equality has been verified experimentally for 2n≤142n\leq14; the stronger question of Schur-positivity with respect to \Des\Des remains unresolved.

References

Primary source

Avichai Marmor, “Schur-Positivity of Short Chords in Matchings”, arXiv:2307.09894 (2026).

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