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Kodaira dimension of moduli of special cubic fourfolds

  • Sho Tanimoto EMAIL logo and Anthony Várilly-Alvarado ORCID logo
Published/Copyright: November 8, 2016

Abstract

A special cubic fourfold is a smooth hypersurface of degree 3 and dimension 4 that contains a surface not homologous to a complete intersection. Special cubic fourfolds give rise to a countable family of Noether–Lefschetz divisors 𝒞d in the moduli space 𝒞 of smooth cubic fourfolds. These divisors are irreducible 19-dimensional varieties birational to certain orthogonal modular varieties. We use the “low-weight cusp form trick” of Gritsenko, Hulek, and Sankaran to obtain information about the Kodaira dimension of 𝒞d. For example, if d=6n+2, then we show that 𝒞d is of general type for n>18, n{20,21,25}; it has nonnegative Kodaira dimension if n>13 and n15. In combination with prior work of Hassett, Lai, and Nuer, our investigation leaves only twenty values of d for which no information on the Kodaira dimension of 𝒞d is known. We discuss some questions pertaining to the arithmetic of K3 surfaces raised by our results.

Funding statement: Tanimoto was partially supported by Lars Hesselholt’s Niels Bohr Professorship. Várilly-Alvarado was supported by NSF grant DMS-1103659 and NSF CAREER grant DMS-1352291.

Acknowledgements

We are grateful to Brendan Hassett for many conversations where he patiently answered our questions, and for his constant encouragement. We thank Klaus Hulek for an illuminating discussion at the Simons Symposium “Geometry over Non-Closed Fields” in March of 2015. We also thank an anonymous referee for their careful reading of the manuscript, and for pertinent suggestions that improved the exposition of the paper. Computer calculations were carried out in Magma [5].

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Received: 2016-08-25
Published Online: 2016-11-08
Published in Print: 2019-07-01

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