Fomin–Fulton–Li–Poon's Schur-positivity conjecture for sorted partitions

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Let λ\lambda and μ\mu be partitions, and let λ∪μ=(ν1,ν2,ν3,…)\lambda\cup\mu=(\nu_1,\nu_2,\nu_3,\ldots) be the partition obtained by rearranging all parts of λ\lambda and μ\mu in weakly decreasing order. Define

sort⁡1(λ,μ)=(ν1,ν3,ν5,…),sort⁡2(λ,μ)=(ν2,ν4,ν6,…).\operatorname{sort}_1(\lambda,\mu)=(\nu_1,\nu_3,\nu_5,\ldots),\qquad \operatorname{sort}_2(\lambda,\mu)=(\nu_2,\nu_4,\nu_6,\ldots).

For symmetric functions ff and gg, f≥sgf\geq_s g means that f−gf-g is Schur nonnegative. Fomin–Fulton–Li–Poon's conjecture.

ssort⁡1(λ,μ)ssort⁡2(λ,μ)≥ssλsμ.s_{\operatorname{sort}_1(\lambda,\mu)}s_{\operatorname{sort}_2(\lambda,\mu)}\geq_s s_\lambda s_\mu.

This conjecture concerns Schur positivity arising from eigenvalue and singular-value inequalities for sums of Hermitian and complex matrices. It was also studied by Bergeron and McNamara, but the source does not specify a resolution status.

References

Primary source

Thomas Lam, Alexander Postnikov and Pavlo Pylyavskyy, “Schur positivity and Schur log-concavity”, arXiv:math/0502446 (2005).

Additional references

3 papers in this index state this conjecture (2004–2005). The statement above is taken from the most recent of them; the others are arXiv:math/0412289, arXiv:math/0403541.

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