# Rationality for generating series for Hilbert scheme of points of curves with toric singularities

More concretely, let $I$ be a monimial ideal in $\mathbb{C}[x_1,\ldots,x_n]$ such that the ring $A=\mathbb{C}[x_1,\ldots,x_n]/I$ is one dimensional. Let $X=\operatorname{Spec}A$, and let $X^{[n]}$ be the punctual Hilbert scheme of points located at the origin. Then is it true that the generating series for Euler characteristic $\sum_{n}\chi(X^{[n]})t^n$ is rational?

• (Do add links from one copy of the question to the other, please) – Mariano Suárez-Álvarez Feb 15 '13 at 20:37

## 1 Answer

The answer is yes in the case that $X$ is reduced. In fact the following more general fact is true (see this recent preprint):

Theorem. Let $X$ be a reduced curve. Then $\sum_n \chi_{mot}(X^{[n]})t^n$ is a rational function where $\chi_{mot}$ is the universal Euler characteristic valued in the Grothendieck ring of varieties $K_0(\mathrm{Var}_\mathbb{C})$.

• How does the fact that $X^[n]$, as defined in this question, restricts the support to the origin affect the answer? – Victor Protsak Jan 10 '18 at 16:33
• @VictorProtsak Right I should have addressed that. The series is still rational. In fact the way we prove the above theorem is by first reducing it to the series for Hilbert schemes supported on a singularity. – Dori Bejleri Jan 10 '18 at 16:42