The asymptotic unimodality conjecture for Kazhdan–Lusztig polynomials

For each nn, let unin\mathrm{uni}_{n} be the proportion of distinct first-row Kazhdan–Lusztig polynomials for Sn\mathrm{S}_{n} that are unimodal, and let uninmult\mathrm{uni}_{n}^{mult} be the corresponding proportion in the multiset of polynomials indexed by Sn\mathrm{S}_{n}. Asymptotic unimodality conjecture. Almost all Kazhdan–Lusztig polynomials are unimodal:

limnunin=limnuninmult=1.\lim_{n\to\infty}\mathrm{uni}_{n}=\lim_{n\to\infty}\mathrm{uni}_{n}^{mult}=1.

The conjecture is motivated by computations and contrasts with the rapidly vanishing proportions of bimodal and trimodal examples observed in the data.

Sources & referencesView supporting material

Primary source

Abel Lacabanne, Daniel Tubbenhauer and Pedro Vaz, “Big data approach to Kazhdan-Lusztig polynomials”, arXiv:2412.01283 (2026).

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