O'Grady's covering-family conjecture for Lagrangian subvarieties

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Let XnX_n be the hyperkähler variety under consideration, let Ωn⊂Xn\Omega_n\subset X_n be the distinguished Lagrangian subvariety, and let a family over a base SS be a morphism π:ZS→Xn\pi:\mathcal{Z}_S\to X_n. Here a Lagrangian subvariety is a subvariety on which the holomorphic symplectic form restricts to zero and whose dimension is half that of XnX_n.

O'Grady's conjecture. There is a positive integer a≥1a\geq 1 and a family of Lagrangian subvarieties π:ZS→Xn\pi:\mathcal{Z}_S\to X_n over a base SS such that ZS\mathcal{Z}_S covers XnX_n, i.e. π\pi is surjective; for all s∈Ss\in S, Zs=∑imiΓi⊂Xn\mathcal{Z}_s=\sum_i m_i\Gamma_i\subset X_n is an effective cycle with each Γi⊂Xn\Gamma_i\subset X_n a Lagrangian subvariety; and there is an s0∈Ss_0\in S such that Zs0=aΩn\mathcal{Z}_{s_0}=a\Omega_n.

This conjecture predicts a covering family whose members include a positive multiple of the distinguished Lagrangian subvariety, as part of the proposed construction of new hyperkähler varieties from Lagrangian subvarieties. Its resolution status is not specified in the supplied text.

References

Primary source

Vanja Zuliani, “Hodge numbers of a Fano eightfold of K3 type”, arXiv:2512.14249 (2026).

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