Volume 23, issue 6 (2019)

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Rationality, universal generation and the integral Hodge conjecture

Mingmin Shen

Geometry & Topology 23 (2019) 2861–2898
Abstract

We use the universal generation of algebraic cycles to relate (stable) rationality to the integral Hodge conjecture. We show that the Chow group of $1$–cycles on a cubic hypersurface is universally generated by lines. Applications are mainly in cubic hypersurfaces of low dimensions. For example, we show that if a generic cubic fourfold is stably rational then the Beauville–Bogomolov form on its variety of lines, viewed as an integral Hodge class on the self product of its variety of lines, is algebraic. In dimensions $3$ and $5$, we relate stable rationality with the geometry of the associated intermediate Jacobian.

Keywords
algebraic cycles, Hodge conjecture, cubic threefold, cubic fourfold
Mathematical Subject Classification 2010
Primary: 14C25, 14C30, 14E08