On the parity conjecture for Hilbert schemes of points on threefolds

Abstract

Let $Hil{b}^d(A^3)$ be the Hilbert scheme of $d$ points in $A^3$, and let $T_z$ denote the tangent space to a point $z\in Hil{b}^d(A^3)$. Okounkov and Pandharipande have conjectured that $\dim T_z$ and $d$ have the same parity for every $z$. For points $z$ parametrizing monomial ideals, the conjecture was proved by Maulik, Nekrasov, Okounkov, and Pandharipande. In this paper, we settle the conjecture for points $z$ parametrizing homogeneous ideals. In fact, we state a generalization of the conjecture to Quot schemes of $A^3$, and we prove it for points parametrizing graded modules.

Final version. To appear on The Annali della Scuola Normale Superiore di Pisa, Classe di Scienze