Cohomology of the Quot scheme of an infinite affine space

Abstract

We study the Quot scheme of points ${\mathrm{Quot}}_d({\mathcal{O}}_{{\mathbb{A}}^n}^{\oplus r})$. We exhibit and compute the cohomology of explicit loci in ${\mathrm{Quot}}_d({\mathcal{O}}_{{\mathbb{A}}^n}^{\oplus r})$, whose complement has codimension diverging to infinity as $n\to \infty$. In the case $1<r<\frac{d+1}{2}$ this loci is an irreducible component. The main ingredient in our proof are classification results on maximal-dimensional spaces of commutative matrices satisfying certain generating conditions. Our primary motivation is the study of the ind-scheme \[ \mathrm{Quot}_d(\mathcal{O}_{\mathbb{A}^{\infty}}^{\oplus r}) := \underset{n\rightarrow \infty}{colim} \mathrm{Quot}_d(\mathcal{O}_{\mathbb{A}^{n}}^{\oplus r}). \] Finally, we compute the cohomology (with integral coefficients) of the Quot scheme ${\mathrm{Quot}}_2({\mathcal{O}}_{{\mathbb{A}}^n}^{\oplus r})$, confirming, in the case $d=2$, a conjecture of Pandharipande.

25 pages, comments welcome!