The Monotone Secant Conjecture for flag manifolds

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Let γ ⁣:R→Rn\gamma\colon\mathbb{R}\to\mathbb{R}^n be a rational normal curve, and let Fℓ(α;n)\mathbb{F}\ell(\alpha;n) be a flag manifold. For a Schubert problem (σ1,…,σm)(\sigma_1,\ldots,\sigma_m), let XσiF∙iX_{\sigma_i}F_{\bullet}^i denote the corresponding Schubert varieties, and call a list of secant flags disjoint when their intervals of secancy are pairwise disjoint and monotone when the order of those intervals agrees with the order of the types of the Grassmannian conditions.

Monotone Secant Conjecture. For any Grassmannian Schubert problem (σ1,…,σm)(\sigma_1,\ldots, \sigma_m) on Fℓ(α;n)\mathbb{F}\ell(\alpha;n) and any disjoint secant flags F∙1,…,F∙mF_{\bullet}^1,\ldots,F_{\bullet}^m that are monotone with respect to the Schubert problem, the intersection

Xσ1F∙1∩Xσ2F∙2∩⋯∩XσmF∙mX_{\sigma_1}F_{\bullet}^1\cap X_{\sigma_2}F_{\bullet}^2\cap\dotsb\cap X_{\sigma_m}F_{\bullet}^m

is transverse and all its points are real. This conjecture extends the Secant Conjecture from Grassmannians to partial flag manifolds; extensive computational experiments support it, but the general assertion remains open.

References

Primary source

Nickolas Hein, Christopher J. Hillar, Abraham Martin del Campo, Frank Sottile and Zach Teitler, “The monotone secant conjecture in the real Schubert calculus”, arXiv:1109.3436 (2014).

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