Complexity of the Zero Set of a Matrix Schubert Ideal
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| Format: | Preprint |
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2025
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| author | Escobar, Laura Meza, Cesar |
| author_facet | Escobar, Laura Meza, Cesar |
| contents | $T$-varieties are normal varieties equipped with an action of an algebraic torus $T$. When the action is effective, the complexity of a $T$-variety $X$ is $\dim(X)-\dim(T)$. Matrix Schubert varieties, introduced by Fulton in 1992, are $T$-varieties consisting of $n \times n$ matrices satisfying certain constraints on the ranks of their submatrices. In this paper, we focus on the complexity of certain torus-fixed affine subvarieties of matrix Schubert varieties. Concretely, given a matrix Schubert variety $\overline{X_{w}}$ where $w\in S_n$, we study the complexity of $Y_w$ obtained by the decomposition $\overline{X_{w}} = Y_{w} \times \mathbb{C}^{k}$ with $k$ as large as possible. Building up from results by Escobar and Mészáros and Donten-Bury, Escobar, and Portakal, we show that for a fixed $n$, the complexity of $Y_{w}$ with respect to this action can be any integer between $0$ and $(n-1)(n-3)$, except $1$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_00131 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Complexity of the Zero Set of a Matrix Schubert Ideal Escobar, Laura Meza, Cesar Algebraic Geometry Combinatorics 05E14, 14N10, 14M12 (Primary), 14M15 (Secondary) $T$-varieties are normal varieties equipped with an action of an algebraic torus $T$. When the action is effective, the complexity of a $T$-variety $X$ is $\dim(X)-\dim(T)$. Matrix Schubert varieties, introduced by Fulton in 1992, are $T$-varieties consisting of $n \times n$ matrices satisfying certain constraints on the ranks of their submatrices. In this paper, we focus on the complexity of certain torus-fixed affine subvarieties of matrix Schubert varieties. Concretely, given a matrix Schubert variety $\overline{X_{w}}$ where $w\in S_n$, we study the complexity of $Y_w$ obtained by the decomposition $\overline{X_{w}} = Y_{w} \times \mathbb{C}^{k}$ with $k$ as large as possible. Building up from results by Escobar and Mészáros and Donten-Bury, Escobar, and Portakal, we show that for a fixed $n$, the complexity of $Y_{w}$ with respect to this action can be any integer between $0$ and $(n-1)(n-3)$, except $1$. |
| title | Complexity of the Zero Set of a Matrix Schubert Ideal |
| topic | Algebraic Geometry Combinatorics 05E14, 14N10, 14M12 (Primary), 14M15 (Secondary) |
| url | https://arxiv.org/abs/2510.00131 |