Zero map between obstruction spaces: subvarieties versus cycles

Abstract

For $Y \subset X$ a locally complete intersection of codimension p, Spencer Bloch [2] constructed the semi-regularity map $π: H^{1}(\mathcal{N}_{Y/X}) \to H^{p+1}(Ω_{X/k}^{p-1})$. As an analogue, we construct a map $\tildeπ: H^{1}(\mathcal{N}_{Y/X}) \to H^{p+1}(Ω_{X/\mathbb{Q}}^{p-1})$, without assuming local complete intersections. While the semi-regularity map $π$ is expected to be injective, we show $\tildeπ$ is a zero map. We use this zero map to interpret how to eliminate obstructions to deforming cycles, an idea by Mark Green and Phillip Griffiths in [9].