Vanishing of Degree 3 Cohomological Invariants

Abstract

For a complex algebraic variety $X$, we show that triviality of the sheaf cohomology group $H^0(X,{\mathcal{H}}^3)$ occurring on the second page of the Bloch-Ogus spectral sequence follows from a condition on the integral Chow group $C{H}^{2}X$ and the integral cohomology group $H^3(X,Z)$. In the case that $X$ is an appropriate approximation to the classifying stack $BG$ of a finite $p$-group $G$, this result states that the group $G$ has no degree three cohomological invariants. As a corollary we show that the nonabelian groups of order $p^3$ for odd prime $p$ have no degree three cohomological invariants.

arXiv comment7 pages; slight generalization of the main result from previous version to apply to a larger class of p-groups