English

A counterexample to the birational Torelli problem for Calabi-Yau threefolds

Algebraic Geometry 2018-03-07 v2

Abstract

The Grassmannian Gr(2,5) is embedded in P9\Bbb{P}^9 via the Pl\"ucker embedding. The intersection of two general PGL(10)-translates of Gr(2,5) is a Calabi-Yau 3-fold X, and the intersection of the projective duals of the two translates is another Calabi-Yau 3-fold Y, deformation equivalent to X. Applying results of Kuznetsov and Jiang-Leung-Xie shows that X and Y are derived equivalent, which by a result of Addington implies that their third cohomology groups are isomorphic as polarised Hodge structures. We show that X and Y provide counterexamples to a certain "birational" Torelli statement for Calabi-Yau 3-folds, namely, they are deformation equivalent, derived equivalent, and have isomorphic Hodge structures, but they are not birational.

Keywords

Cite

@article{arxiv.1706.09952,
  title  = {A counterexample to the birational Torelli problem for Calabi-Yau threefolds},
  author = {John Christian Ottem and Jørgen Vold Rennemo},
  journal= {arXiv preprint arXiv:1706.09952},
  year   = {2018}
}

Comments

13 pages; Minor changes