Semiorthogonal decomposition conjecture for Fano schemes of lines on intersections of two quadrics

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Let X=Q1∩Q2⊂Pn+2X=Q_1\cap Q_2\subset\mathbb{P}^{n+2} be a smooth complete intersection of two quadrics in an odd-dimensional projective space. Let CC be the hyperelliptic curve associated with the pencil of quadrics, branched over its singular quadrics, and let F1(X)F_1(X) denote the Fano variety of lines on XX. Semiorthogonal decomposition conjecture. There is a semiorthogonal decomposition

Db(F1(X))=⟨Db(Sym⁡2C),Db(C),…,Db(C)⏟n−3 times,Db(C),…,Db(C)⏟(n−42)+2(n−4) times⟩.\mathrm{D}^{\mathrm{b}}(F_1(X))=\left\langle\mathrm{D}^{\mathrm{b}}(\operatorname{Sym}^2 C),\underbrace{\mathrm{D}^{\mathrm{b}}(C),\dots,\mathrm{D}^{\mathrm{b}}(C)}_{n-3\text{ times}},\underbrace{\mathrm{D}^{\mathrm{b}}(\mathbb{C}),\dots,\mathrm{D}^{\mathrm{b}}(\mathbb{C})}_{{n-4\choose 2}+2(n-4)\text{ times}}\right\rangle.

This is the specialization of a broader conjecture on semiorthogonal decompositions for Fano schemes of linear spaces on intersections of quadrics. The paper uses it as input for the subsequent orthogonal-Grassmannian conjecture; its resolution status is not specified in the supplied text.

References

Primary source

Saket Shah, “Flips for spaces of quadrics on del Pezzo varieties”, arXiv:2602.07366 (2026).

Additional references

3 papers in this index state this conjecture (2021–2026). The statement above is taken from the most recent of them; the others are arXiv:2311.00355, arXiv:2108.13353.

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