Asymptotic independence of descent sets and being an n-cycle

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For each nn, let [n−1]={1,…,n−1}[n-1]=\{1,\ldots,n-1\}, and let βn(I)\beta_n(I) denote the number of permutations in SnS_n with descent set I⊆[n−1]I\subseteq[n-1], while βncyc(I)\beta^{\mathrm{cyc}}_n(I) denotes the number of nn-cycles with descent set II. Asymptotic independence conjecture.

lim⁡n→∞max⁡∅⫋I⫋[n−1]∣n βncyc(I)βn(I)−1∣=0.\lim_{n\to\infty}\max_{\varnothing \subsetneqq I \subsetneqq [n-1]} \left| \frac{n\, \beta^{\mathrm{cyc}}_n(I)}{\beta_n(I)} - 1\right| = 0.

This asserts that, uniformly over all non-empty proper descent sets, having descent set II and being an nn-cycle are asymptotically independent, with the proportion of nn-cycles tending to 1/n1/n as it does among all permutations. The source presents this as a conjectural strengthening of the known asymptotic independence result for alternating permutations.

References

Primary source

Sergi Elizalde and Justin M. Troyka, “Exact and asymptotic enumeration of cyclic permutations according to descent set”, arXiv:1710.05103 (2019).

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