Lyubeznik's étale cohomological dimension conjecture

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Let UU be a scheme of finite type over a separably closed field K\mathbb{K}. Write eˊcd⁡(U)\operatorname{\acute{e}cd}(U) for its étale cohomological dimension and qccd⁡(U)\operatorname{qccd}(U) for its quasicoherent cohomological dimension.

Lyubeznik's conjecture.

eˊcd⁡(U)≥dim⁡(U)+qccd⁡(U).\operatorname{\acute{e}cd}(U) \geq \dim(U)+\operatorname{qccd}(U).

The conjecture compares étale and quasicoherent cohomological dimensions. It was motivated by examples in which the étale-cohomological lower bound is at least as strong as the quasicoherent one; its resolution is not specified here.

References

Primary source

Manolis C. Tsakiris and Matteo Varbaro, “Étale and Quasicoherent Cohomological Dimensions of Subspace Arrangements”, arXiv:2606.20448 (2026).

Additional references

4 papers in this index state this conjecture (2010–2026). The statement above is taken from the most recent of them; the others are arXiv:2106.09796, arXiv:1011.6648, arXiv:1007.5440.

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