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

Farkas, Pandharipande, and Sammartano constructed non-rational irreducible components of Hilbert schemes of points in affine space ${\mathbb{A}}^n$ for all $n\ge 12$. 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 $g_9^3$ curve source. As a consequence, over a field of characteristic zero, $\mathrm{Hilb}({\mathbb{A}}^n)$ has non-rational irreducible components for all $n\ge 10$.