Bijective proof of major-index palindromicity
Construct, for every partition \(\lambda\) of \(N\), an explicit bijection \(\Phi:\SYT(\lambda)\to\SYT(\lambda)\) satisfying \(\maj(T)+\maj(\Phi(T))=\binom{N}{2}+b(\lambda)-b(\lambda')\) for every standard Young tableau \(T\) of shape \(\lambda\).
References
It follows from equation~eq:HLF that these polynomials are palindromic. However, no bijective proof of this fact seems to be known.
eq:HLF:
$\sum_{T\in\SYT(\lambda)} q^{\maj(T)}=q^{b(\lambda)}\frac{[N]_q!}{\prod_{c\in\lambda}[h_c]_q!}, $
— Symmetry of ascent and descent distributions on rectangular and staircase tableaux
(2501.07573 - Elizalde, 13 Jan 2025) in Section 1 of Section 6, “Symmetry of the major index,” Problem 6.1 (labelled prob:maj)