The hyper-Kummer construction

Abstract

The hyper-Kummer construction, discovered by the first-named author, associates a hyper-Kähler manifold of $\mathrm{K}3^{[3]}$-type with any hyper-Kähler sixfold of generalized Kummer type. We regard this construction as a higher-dimensional analog of the classical Kummer construction of K3 surfaces from abelian surfaces. In this spirit, we prove several results which parallel those known for the classical Kummer construction: we characterize the hyper-Kummer $\mathrm{K}3^{[3]}$-manifolds up to birational equivalence in terms of their Hodge lattices, and establish a McKay correspondence for their derived categories and Chow motives. We propose a recipe to construct locally complete families of projective varieties of $\mathrm{Kum}^3$-type starting from a family of varieties of $\mathrm{K}3^{[3]}$-type equipped with 16 prime divisors in a certain Kummer lattice configuration. We also compare hyper-Kummer $\mathrm{K}3^{[3]}$-manifolds with the Mongardi-Rapagnetta-Saccà double covers of O'Grady's six-dimensional hyper-Kähler manifolds. The hyper-Kummer construction produces a rich configuration of hyper-Kähler manifolds of $\mathrm{K}3^{[2]}$-type and K3 surfaces canonically associated with a manifold of $\mathrm{Kum}^3$-type, in particular the hyper-Kummer K3 surfaces, which form countably many $4$-dimensional families of generic Picard rank 16. We prove abelianity of Chow motives for infinitely many 4-dimensional families of hyper-Kummer K3 surfaces, thereby proving Kimura-O'Sullivan finite-dimensionality conjecture for many new K3 surfaces of Picard rank 16. As other applications, we prove Beauville's weak splitting conjecture for all varieties of $\mathrm{Kum}^3$-type, and, building on previous results, we prove the Hodge and Tate conjectures for all powers of any of the varieties involved in the hyper-Kummer construction.