The generalized Franchetta conjecture for some hyper-Kähler varieties, II

The generalized Franchetta conjecture for some hyper-Kähler varieties

The generalized Franchetta conjecture for hyper-Kähler varieties predicts that an algebraic cycle on the universal family of certain polarized hyper-Kähler varieties is fiberwise rationally equivalent to zero if and only if it vanishes in cohomology fiberwise. We establish Franchetta-type results for certain low (Hilbert) powers of low degree K3 surfaces, for the Beauville--Donagi family of Fano varieties of lines on cubic fourfolds and its relative square, and for $0$-cycles and codimension-$2$ cycles for the Lehn--Lehn--Sorger--van Straten family of hyper-Kähler eightfolds. We also draw many…

A remark on the generalized Franchetta conjecture for K3 surfaces

A family of K3 surfaces $\mathscr{X}\rightarrow B$ has the \emph{Franchetta property} if the Chow group of 0-cycles on the generic fiber is cyclic. The generalized Franchetta conjecture proposed by O'Grady asserts that the universal family $\mathscr{X}_g\rightarrow \mathscr{F}_g$ of polarized K3 of degree $2g-2$ has the Franchetta property. While this is known only for small $g$ thanks to \cite{PSY}, we prove that for all $g$ there is a hypersurface in $ \mathscr{F}_g$ such that the corresponding family has the Franchetta property.

ACM丛的Hodge秩与Franchetta猜想

Hodge rank of ACM bundles and Franchetta's conjecture

本文证明一般高维超曲面上低正则性ACM丛中非平凡Hodge类蕴含平凡直和项，并由此推出次数不低于3、维数至少4的光滑超曲面族不存在通用Ulrich丛，给出Franchetta型结论。

Beauville-Voisin-Franchetta 猜想与 LLSS 八重形

The Beauville-Voisin-Franchetta conjecture and LLSS eightfolds

本文提出融合 Beauville-Voisin 与 Franchetta 的猜想，给出其由标准猜想、Murre (D) 和 X^3 的 Franchetta 猜想推出的条件，并证明其对 LLSS 八重形的余维 2、8 闭链成立。

Cotangent bundles of toric varieties and coverings of toric hyperkähler manifolds

Toric hyperk{ä}hler manifolds are quaternion analog of toric varieties. Bielawski pointed out that they can be glued by cotangent bundles of toric varieties. Following his idea, viewing both toric varieties and toric hyperk{ä}her manifolds as GIT quotients, we first establish geometrical criteria for the semi-stable points. Then based on these criteria, we show that the cotangent bundles of compact toric varieties in the core of toric hyperk{ä}hler manifold are sufficient to glue the desired toric hyperk{ä}hler manifold.

Very symmetric hyper-Kähler fourfolds

G. Höhn and G. Mason classified all finite groups acting faithfully and symplectically on a hyper-K{ä}hler fourfolds of type K3$^{[2]}$. There are 15 maximal among them, call them $\widetilde{G}_1,\ldots, \widetilde{G}_{15}$. Every manifold of type K3$^{[2]}$ admitting an action of $\widetilde{G}_i$ for some $i$ must necessarily have Picard rank 21 which is maximal. This fact allows us to use lattice-theoretic methods to classify all the finite groups $G$ acting faithfully on a hyper-K{ä}hler fourfold of type K3$^{[2]}$ $X$ such that $G$ contains $\widetilde{G}_i$ as a proper subgroup and $\wi…