Components and singularities of Quot schemes and varieties of commuting matrices

TL;DR

This paper classifies the components of the variety of commuting matrices and Quot schemes of points, revealing when they are reduced or nonreduced, using deformation methods and algebraic techniques.

Contribution

It provides a comprehensive classification of components for commuting matrix varieties and Quot schemes up to degree 7, and introduces methods to analyze their structure.

Findings

Components are classified for matrices of size up to 7.

Starting from size 8, the scheme has nonreduced components.

Up to degree 7, the scheme is generically reduced.

Abstract

We investigate the variety of commuting matrices. We classify its components for any number of matrices of size at most 7. We prove that starting from quadruples of size 8 matrices, this scheme has generically nonreduced components, while up to degree 7 it is generically reduced. Our approach is to recast the problem as deformations of modules and generalize an array of methods: apolarity, duality and Bia\l{}ynicki-Birula decompositions to this setup. We include a thorough review of our methods to make the paper self-contained and accessible to both algebraic and linear-algebraic communities. Our results give the corresponding statements for the Quot schemes of points, in particular we classify the components of $Quot_d(O_{\mathbb{A}^n}^{\oplus r})$ for $d\leq 7$ and all $r$, $n$.