Hyper-Kähler fourfolds and Kummer surfaces

Iliev, Atanas; Kapustka, Grzegorz; Kapustka, Michal; Ranestad, Kristian

doi:10.1112/plms.12063

Cited by 20 publications

(26 citation statements)

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“…(ii) As explained in [21, 9.8], the Verra threefold (and hence also the Verra fourfold) can be reconstructed starting from (S j , α j ). (Alternatively, the period map for double EPW quartics has 19-dimensional image [25]. Thus, to a general point in the period domain (corresponding to a general genus 2 K3 surface), one can associate a double EPW quartic Z, and to a general Z one can in turn associate a Verra fourfold X according to [25,Theorem 0.2].)…”

Section: (Ii) a Very General Genus 2 K3 Surface Is Related In This Wamentioning

confidence: 99%

“…(Alternatively, the period map for double EPW quartics has 19-dimensional image [25]. Thus, to a general point in the period domain (corresponding to a general genus 2 K3 surface), one can associate a double EPW quartic Z, and to a general Z one can in turn associate a Verra fourfold X according to [25,Theorem 0.2].) (iii) For very general X, the Hodge structure H 4 tr (X) admits a unique polarization up to a non-zero coefficient.…”

Section: (Ii) a Very General Genus 2 K3 Surface Is Related In This Wamentioning

confidence: 99%

“…Corollary 2.5). Also, both cubic fourfolds and Verra fourfolds are related (via an Abel-Jacobi isomorphism) to hyperkähler fourfolds: for the first, this is the famous [7]; for the second, this is the more recent [25].…”

Section: Introductionmentioning

confidence: 99%

“…, which implies in particular that there is an isomorphism f Lasz : H 4 tr (X, Q) ∼ = − → H 2 tr (S, Q) (1) . On the other hand, it is known [25,Proposition 4.1] that the double EPW quartic Z associated to X is isomorphic to the moduli space of twisted stable sheaves on the K3 surface S (such moduli spaces are constructed in [61]):…”

Section: Introductionmentioning

confidence: 99%

“…Remark 2.6. To further the analogy with cubic fourfolds, we remark that the general Verra fourfold is suspected to be irrational [25,Remark 4.2]. Certain special Verra fourfolds are known to be rational [12,Corollary 6.4].…”

Section: Introductionmentioning

confidence: 99%

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Algebraic cycles and very special cubic fourfolds

Laterveer

2019

Indagationes Mathematicae

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This note is about the Chow ring of Verra fourfolds. For a general Verra fourfold, we show that the Chow group of homologically trivial 1-cycles is generated by conics. We also show that Verra fourfolds admit a multiplicative Chow-Künneth decomposition, and draw some consequences for the intersection product in the Chow ring of Verra fourfolds. 1 2 ROBERT LATERVEERCorollary (=Corollary 5.3). Let X be any Verra fourfold. The subalgebrainjects into cohomology via the cycle class map. (Here, c j (T X ) are the Chow-theoretic Chern classes.) (This can be generalized to self-products X m , cf. Corollary 5.6.) The construction of a multiplicative Chow-Künneth decomposition relies once more on the spread argument, by first showing (Theorem 4.8) that any Verra fourfold can be motivically related to a genus 2 K3 surface. This close link to K3 surfaces also has the following consequence:Corollary (=Corollary 5.9). Let X, X ′ be two Verra fourfolds that are isogenous (i.e., there exists an isomorphism of Q-vector spaces H 4 (X, Q) ∼ = H 4 (X ′ , Q) compatible with the Hodge structures and with cup product). Then there is an isomorphism of Chow motivesFurther consequences concern a multiplicative decomposition in the derived category (Corollary 5.12), the generalized Hodge conjecture for self-products, and finite-dimensionality of the motive of certain special Verra fourfolds (Corollary 5.14).Conventions. In this note, the word variety will refer to a reduced irreducible scheme of finite type over C. For any n-dimensional variety X, we will write A i (X) for the Chow group of dimension i cycles on X with Q-coefficients, and A j (X) for the operational Chow cohomology of [17] with Q-coefficients (this can be identified with A n−j (X) for smooth X).The notations A j hom (X) and A j AJ (X) will indicate the subgroups of homologically trivial (resp. Abel-Jacobi trivial) cycles.For a morphism between smooth varieties f : X → Y , we will write Γ f ∈ A * (X × Y ) for the graph of f , and t Γ f ∈ A * (Y × X) for the transpose correspondence.The contravariant category of Chow motives (i.e., pure motives with respect to rational equivalence as in [43], [39]) will be denoted M rat .We will write H * (X) = H * (X, Q) for singular cohomology with Q-coefficients. VERRA FOURFOLDSDefinition 2.1 ([50]). A Verra fourfold is a double cover of P 2 × P 2 branched along a smooth divisor of bidegree (2, 2). Remark 2.2. The moduli space of Verra fourfolds is 19-dimensional [25, Section 0.3]. Lemma 2.3. A Verra fourfold X is a Fano variety (i.e., the canonical bundle is anti-ample). In particular, A 4 (X) = Q and the Hodge conjecture is true for X. Proof. The canonical bundle formula shows that X is Fano. Fano varieties are rationally connected [13], [30], and so A 4 (X) = Q. The Hodge conjecture is known for fourfolds with trivial Chow group of 0-cycles [10].

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Section: (Ii) a Very General Genus 2 K3 Surface Is Related In This Wamentioning

confidence: 99%

Section: (Ii) a Very General Genus 2 K3 Surface Is Related In This Wamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%