The Shapiro conjecture for the orthogonal Grassmannian

Let OG(n)OG(n) be the orthogonal Grassmannian, let F(t)F_\bullet(t) be the isotropic flag osculating a specified rational normal curve, and let XκFX_{\boldsymbol{\kappa}}F_\bullet denote the Schubert variety indexed by a strict partition κ\boldsymbol{\kappa}. A Schubert problem (κ1,,κm)({\boldsymbol{\kappa}}_1,\dotsc,{\boldsymbol{\kappa}}_m) satisfies

κ1++κm=dimOG(n)=(n+12).\|{\boldsymbol{\kappa}}_1\|+\dotsb+\|{\boldsymbol{\kappa}}_m\|=\dim OG(n)=\binom{n+1}{2}.

The Shapiro conjecture for OG(n)OG(n). If s1,,sms_1,\dotsc,s_m are distinct real numbers, then

Xκ1F(s1)XκmF(sm)X_{{\boldsymbol{\kappa}}_1}F_\bullet(s_1)\cap\dotsb\cap X_{{\boldsymbol{\kappa}}_m}F_\bullet(s_m)

is transverse and all its points are real. This is an orthogonal-Grassmannian analogue of the Grassmannian Shapiro conjecture; unlike the Grassmannian case, the source presents it as an open conjecture.

Sources & referencesView supporting material

Primary source

Frank Sottile, “Frontiers of Reality in Schubert Calculus”, arXiv:0907.1847 (2009).

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