Preprints
- Laura Escobar and Cesar J. Meza. Complexity of the zero set of a matrix Schubert ideal. Sept. 2025. DOI: 10.48550/arXiv.2510.00131.Abstract: $T$-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–Mészáros and Donten-Bury–Escobar–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 $1$.