A One-Variable Frame Construction For Irrational Components of Hilbert Schemes of Points

Abstract

Farkas, Pandharipande, and Sammartano constructed non-rational irreducible components of Hilbert schemes of points in affine space $\mathbb{A}^n$ for all $n \geq 12$. Their construction starts from Hilbert schemes of curves in $\mathbb{P}^3$, adjoins two auxiliary variables in order to apply Jelisiejew's TNT frame construction, and then doubles the number of variables. We give a one-variable variant of the construction. The new input is a local-cohomology replacement for the depth-three step in Jelisiejew's negative tangent computation. It uses the vanishing of the low-degree Hartshorne--Rao module for the complete $g^3_9$ curve source. As a consequence, over a field of characteristic zero, $\operatorname{Hilb}(\mathbb{A}^n)$ has non-rational irreducible components for all $n \geq 10$.