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 \(\lambda\).

Background

The paper considers the major index $\maj(T)=\sum_{i\in\Des(T)}i$ on standard Young tableaux. Stanley’s qq-analogue of the hook-length formula gives the generating polynomial for this statistic and implies that the polynomial is palindromic, but the paper notes that a bijective proof of this palindromicity is not known.

The requested bijection should pair tableaux of the same shape so that their major indices sum to the stated constant (N2)+b(λ)b(λ)\binom{N}{2}+b(\lambda)-b(\lambda'). The paper observes that evacuation proves symmetry on subsets with a fixed number of descents, but does not solve the problem globally for all tableaux of a given shape.

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)