Multiplicative Chow-K\"unneth decompositions and varieties of cohomological K3 type

Abstract

Given a smooth projective variety, a Chow-K\"unneth decomposition is called multiplicative if it is compatible with the intersection product. Following works of Beauville and Voisin, Shen and Vial conjectured that hyper-K\"ahler varieties admit a multiplicative Chow-K\"unneth decomposition. In this paper, based on the mysterious link between Fano varieties with cohomology of K3 type and hyper-K\"ahler varieties, we ask whether Fano varieties with cohomology of K3 type also admit a multiplicative Chow-K\"unneth decomposition, and provide evidence by establishing their existence for cubic fourfolds and K\"uchle fourfolds of type c7. The main input in the cubic hypersurface case is the Franchetta property for the square of the Fano variety of lines; this was established in our earlier work in the fourfold case and is generalized here to arbitrary dimension. On the other end of the spectrum, we also give evidence that varieties with ample canonical class and with cohomology of K3 type might admit a multiplicative Chow-K\"unneth decomposition, by establishing this for two families of Todorov surfaces.