Standard monomial theory and toric degenerations of Schubert varieties from matching field tableaux

On multiplicities of points on Schubert varieties in Grassmannians

We answer some questions related to multiplicity formulas by Rosenthal and Zelevinsky and by Lakshmibai and Weyman for points on Schubert varieties in Grassmannians. In particular, we give combinatorial interpretations in terms of nonintersecting lattice paths of these formulas, which makes the equality of the two formulas immediately obvious. Furthermore we provide an alternative determinantal formula for these multiplicities, and we show that they count semistandard tableaux of unusual shapes.

Standard monomial theory and toric degenerations of Richardson varieties inside Grassmannians and flag varieties

We study toric degenerations of opposite Schubert and Richardson varieties inside degenerations of Grassmannians and flag varieties. These degenerations are parametrized by matching fields in the sense of Sturmfels and Zelevinsky. We construct so-called restricted matching field ideals whose generating sets are understood combinatorially through tableaux. We determine when these ideals are toric and coincide with Gröbner degenerations of Richardson varieties using the well established standard monomial theory for Grassmannians and flag varieties.

Standard monomial theory and toric degenerations of Richardson varieties in the Grassmannian

Richardson varieties are obtained as intersections of Schubert and opposite Schubert varieties. We provide a new family of toric degenerations of Richardson varieties inside Grassmannians by studying Gröbner degenerations of their corresponding ideals. These degenerations are parametrised by block diagonal matching fields in the sense of Sturmfels-Zelevinsky. We associate a weight vector to each block diagonal matching field and study its corresponding initial ideal. In particular, we characterise when such ideals are toric, hence providing a family of toric degenerations for Richardson variet…

无碰撞管道梦编码 Schubert 多项式的 Gröbner 几何

Bumpless pipe dreams encode Gröbner geometry of Schubert polynomials

本文证明无碰撞管道梦可按对角项序为矩阵 Schubert 簇的对角 Gröbner 退化不可约分量索引，证实相关猜想并确立其与经典管道梦的对偶几何地位。

Standard monomial theory and toric degenerations of Richardson varieties in flag varieties

We study standard monomial bases for Richardson varieties inside the flag variety. In general, writing down a standard monomial basis for a Richardson variety can be challenging, as it involves computing so-called defining chains or key tableaux. However, for a certain family of Richardson varieties, indexed by compatible permutations, we provide a very direct and straightforward combinatorial rule for writing down a standard monomial basis. We apply this result to the study of toric degenerations of Richardson varieties. In particular, we provide a new family of toric degenerations of Richard…

Seshadri 分层与标准单项式理论

Seshadri stratifications and standard monomial theory

本文提出嵌入射影簇上的 Seshadri 分层，用以构造 Newton-Okounkov 单纯复形与平坦环面退化，并为标准单项式理论及 Schubert 簇中 LS 路径的几何解释提供统一框架。