Kuznetsov–Smirnov's quantum-spectrum conjecture for Fano varieties

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Let XX be a Fano variety of index mm over an algebraically closed field k\boldsymbol{\Bbbk} of characteristic zero, and assume that the big quantum cohomology BQH⁡(X)\operatorname{BQH}(X) is generically semisimple. Let QS⁡X×\operatorname{QS}^{\times}_X and QS⁡X∘\operatorname{QS}^{\circ}_X denote the nonzero and zero parts, respectively, of the quantum spectrum, and let Aut⁡(X)\operatorname{Aut}(X) act on XX and its derived category. A rectangular Lefschetz collection has blocks indexed by twists 0,…,m−10,\ldots,m-1, and its residual category is the orthogonal complement of these blocks. Kuznetsov–Smirnov's conjecture. There is an Aut⁡(X)\operatorname{Aut}(X)-invariant exceptional collection E1,…,EkE_1,\dots,E_k in Db(X)\mathbf D^{\mathrm b}(X), where kk is the length of QS⁡X×\operatorname{QS}^{\times}_X divided by mm, extending to the rectangular Lefschetz collection

E1,…,Ek;E1(1),…,Ek(1);… ;E1(m−1),…,Ek(m−1)E_1,\dots,E_k; E_1(1),\dots,E_k(1); \dots; E_1(m-1),\dots,E_k(m-1)

in Db(X)\mathbf D^{\mathrm b}(X). Its residual category R\mathcal R has a completely orthogonal Aut⁡(X)\operatorname{Aut}(X)-invariant decomposition

R=⨁ξ∈QS⁡X∘Rξ,\mathcal R=\bigoplus_{\xi\in\operatorname{QS}^{\circ}_X}\mathcal R_\xi,

where the components are indexed by closed points ξ∈QS⁡X∘\xi\in\operatorname{QS}^{\circ}_X, and Rξ\mathcal R_\xi is generated by an exceptional collection whose length equals the length of the localization (QS⁡X∘)ξ(\operatorname{QS}^{\circ}_X)_\xi at ξ\xi. Finally, the induced polarization τR\tau_{\mathcal R} sends Rξ\mathcal R_\xi equivalently to Rg(ξ)\mathcal R_{g(\xi)} for each ξ\xi, where gg is a generator of μm\mu_m. These predictions relate the quantum cohomology spectrum of a Fano variety to its Lefschetz decomposition and residual category; their general validity is not established.

References

Primary source

Maxim Smirnov, “Residual categories of Grassmannians”, arXiv:2212.01580 (2022).

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