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UNIVERSAL GRAPH SCHUBERT VARIETIES

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Abstract

We consider the loci of invertible linear maps f : ℂn → (ℂn)* together with pairs of flags (E•, F•) in ℂn such that the various restrictions f : Fj → \( {E}_i^{\ast } \) have specified ranks. Identifying an invertible linear map with its graph viewed as a point in a Grassmannian, we show that the closures of these loci have cohomology classes represented by the back-stable Schubert polynomials of Lam, Lee, and Shimozono. As a special case, we recover the result of Knutson, Lam, and Speyer that Stanley symmetric functions represent the classes of graph Schubert varieties.

We consider similar loci where f is restricted to be symmetric or skew-symmetric. Their classes are now given by back-stable versions of the polynomials introduced by Wyser and Yong to represent classes of orbit closures for the orthogonal and symplectic groups acting on the type A flag variety. Using degeneracy locus formulas of Kazarian and of Anderson and Fulton, we obtain new Pfaffian formulas for these polynomials in the vexillary case. We also give a geometric interpretation of the involution Stanley symmetric functions of Hamaker, Marberg, and the author: they represent classes of involution graph Schubert varieties in isotropic Grassmannians.

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    BRENDAN PAWLOWSKI

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PAWLOWSKI, B. UNIVERSAL GRAPH SCHUBERT VARIETIES. Transformation Groups 26, 1417–1461 (2021). https://doi.org/10.1007/s00031-021-09677-6

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