The motive of the Hilbert scheme of points in all dimensions

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Main Authors: Graffeo, Michele, Monavari, Sergej, Moschetti, Riccardo, Ricolfi, Andrea T.
Format: Preprint
Published: 2024
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author Graffeo, Michele
Monavari, Sergej
Moschetti, Riccardo
Ricolfi, Andrea T.
author_facet Graffeo, Michele
Monavari, Sergej
Moschetti, Riccardo
Ricolfi, Andrea T.
contents We prove a closed formula for the generating function $\mathsf Z_d(t)$ of the motives $[\mathrm{Hilb}^d(\mathbb A^n)_0] \in K_0(\mathrm{Var}_{\mathbb C})$ of punctual Hilbert schemes, summing over $n$, for fixed $d>0$. The result is an expression for $\mathsf Z_d(t)$ as the product of the zeta function of $\mathbb P^{d-1}$ and a polynomial $\mathsf P_d(t)$, which in particular implies that $\mathsf Z_d(t)$ is a rational function. Moreover, we reduce the complexity of $\mathsf P_d(t)$ to the computation of $d-8$ initial data, and therefore give explicit formulas for $\mathsf Z_d(t)$ in the cases $d \leq 8$, which in turn yields a formula for $[\mathrm{Hilb}^{\leq 8}(X)]$ for any smooth variety $X$. We perform a similar analysis for the Quot scheme of points, obtaining explicit formulas for the full generating function (summing over all ranks and dimensions) for $d \leq 4$. In the limit $n \to \infty$, we prove that the motives $[\mathrm{Hilb}^d(\mathbb A^n)_0]$ stabilise to the class of the infinite Grassmannian $\mathrm{Gr}(d-1,\infty)$. Finally, exploiting our geometric methods, we conjecture (and partially confirm) a structural result on the 'error' measuring the discrepancy between the count of higher dimensional partitions and MacMahon's famous guess.
format Preprint
id arxiv_https___arxiv_org_abs_2406_14321
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle The motive of the Hilbert scheme of points in all dimensions
Graffeo, Michele
Monavari, Sergej
Moschetti, Riccardo
Ricolfi, Andrea T.
Algebraic Geometry
We prove a closed formula for the generating function $\mathsf Z_d(t)$ of the motives $[\mathrm{Hilb}^d(\mathbb A^n)_0] \in K_0(\mathrm{Var}_{\mathbb C})$ of punctual Hilbert schemes, summing over $n$, for fixed $d>0$. The result is an expression for $\mathsf Z_d(t)$ as the product of the zeta function of $\mathbb P^{d-1}$ and a polynomial $\mathsf P_d(t)$, which in particular implies that $\mathsf Z_d(t)$ is a rational function. Moreover, we reduce the complexity of $\mathsf P_d(t)$ to the computation of $d-8$ initial data, and therefore give explicit formulas for $\mathsf Z_d(t)$ in the cases $d \leq 8$, which in turn yields a formula for $[\mathrm{Hilb}^{\leq 8}(X)]$ for any smooth variety $X$. We perform a similar analysis for the Quot scheme of points, obtaining explicit formulas for the full generating function (summing over all ranks and dimensions) for $d \leq 4$. In the limit $n \to \infty$, we prove that the motives $[\mathrm{Hilb}^d(\mathbb A^n)_0]$ stabilise to the class of the infinite Grassmannian $\mathrm{Gr}(d-1,\infty)$. Finally, exploiting our geometric methods, we conjecture (and partially confirm) a structural result on the 'error' measuring the discrepancy between the count of higher dimensional partitions and MacMahon's famous guess.
title The motive of the Hilbert scheme of points in all dimensions
topic Algebraic Geometry
url https://arxiv.org/abs/2406.14321