Antichain polynomials of products of chains and minuscule posets
Abstract
This paper studies the antichain polynomials of [k]× P, where P is a connected minuscule poset. We give a formula for the number of antichains, counted by size, of an arbitrary poset. Using this formula, we present necessary and sufficient conditions for the palindromicity of antichain polynomials for two infinite families of connected minuscule posets. We show that, for every connected minuscule poset P, if the antichain polynomial of [k]× P is palindromic, then it has only real and strictly negative zeros. This result, in particular, gives an affirmative answer to Ding-Dong's conjecture about γ-positivity of the antichain polynomial of [k]× P. By constructing a bijection between antichains and labeled Dyck paths, we also give a layer-refined enumeration of the antichains in [2]×[m]×[n]. We establish a relation between such antichains and Clar covers of the hexagonal flakes O(2,m,n), thus prove a conjectured determinantal formula for a family of Zhang-Zhang polynomials. Real-rootedness and stability results are also obtained when the shortest chain has length at most two. Finally, we present infinitely many connected Peck posets whose antichain polynomials are not unimodal, disproving the log-concavity conjecture of Ding and Dong.
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BibTeX
@misc{chen2026antichain,
title = {{Antichain polynomials of products of chains and minuscule posets}},
author = {Xi Chen and Yuxian Dong and Sihao Tang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28983},
eprint = {2609.28983},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28983},
}
RIS
TY - UNPB
TI - Antichain polynomials of products of chains and minuscule posets
AU - Xi Chen
AU - Yuxian Dong
AU - Sihao Tang
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.28983
UR - https://arxiv.org/abs/2609.28983
AB - This paper studies the antichain polynomials of [k]× P, where P is a connected minuscule poset. We give a formula for the number of antichains, counted by size, of an arbitrary poset. Using this formula, we present necessary and sufficient conditions for the palindromicity of antichain polynomials for two infinite families of connected minuscule posets. We show that, for every connected minuscule poset P, if the antichain polynomial of [k]× P is palindromic, then it has only real and strictly negative zeros. This result, in particular, gives an affirmative answer to Ding-Dong's conjecture about γ-positivity of the antichain polynomial of [k]× P. By constructing a bijection between antichains and labeled Dyck paths, we also give a layer-refined enumeration of the antichains in [2]×[m]×[n]. We establish a relation between such antichains and Clar covers of the hexagonal flakes O(2,m,n), thus prove a conjectured determinantal formula for a family of Zhang-Zhang polynomials. Real-rootedness and stability results are also obtained when the shortest chain has length at most two. Finally, we present infinitely many connected Peck posets whose antichain polynomials are not unimodal, disproving the log-concavity conjecture of Ding and Dong.
ER -