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arXiv · 2508.20337

Combinatorial proof of a permuted basement Macdonald polynomial identity

Daniel Orr·Johnny Rivera Jr
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Abstract

A well-known and fundamental property of the Macdonald polynomials $P_\lambda(x;q,t)$ is their invariance under the transformation sending $(q,t)$ to $(q^{-1},t^{-1})$. Recently, Concha and Lapointe showed that this property extends in an interesting, nontrivial way to an identity for partially symmetric Macdonald polynomials. Their identity played a key role in the work of Bechtloff Weising and Orr linking partially symmetric Macdonald polynomials to parabolic flag Hilbert schemes. In this paper, we refine the Concha-Lapointe identity to a sub-family of Alexandersson's permuted basement Macdonald polynomials and give a combinatorial proof of the refined identity. We show also that the Concha-Lapointe identity is equivalent to the assertion that (normalized) partially symmetric Macdonald polynomials are fixed under the Kazhdan-Lusztig involution.

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Daniel Orr, Johnny Rivera Jr. 2025-08-28. Combinatorial proof of a permuted basement Macdonald polynomial identity. https://arxiv.org/abs/2508.20337

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