The categorical crepant resolution conjecture for Pfaffian varieties

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Let VV be an nn-dimensional vector space, with nn even, and let kk be an integer. Write Pf(2k,V∨){\mathrm {Pf}}(2k,V^{\vee}) and Pf(n−2k,V){\mathrm {Pf}}(n-2k,V) for the corresponding Pfaffian varieties, and let D~b\widetilde{D}^b denote their categorical crepant resolutions. A Lefschetz decomposition consists of admissible blocks Ai\mathcal{A}_i or Bi\mathcal{B}_i with the indicated twists.

Categorical crepant resolution conjecture. The categorical crepant resolution D~b(Pf(2k,V∨))\widetilde{D}^b({\mathrm {Pf}}(2k,V^{\vee})) has the non-rectangular Lefschetz decomposition

D~b(Pf(2k,V∨))=⟨A0,A1(1), ⋯ ,Ank−n2−1(nk−n2−1), Ank−n2(nk−n2), ⋯ ,Ank−1(nk−1)⟩,\widetilde{D}^b({\mathrm {Pf}}(2k,V^{\vee}))=\Big\langle \mathcal{A}_{0}, \mathcal{A}_{1}(1),\ \cdots,\mathcal{A}_{nk-\frac{n}{2}-1}(nk-\frac{n}{2}-1),\ \mathcal{A}_{nk-\frac{n}{2}}(nk-\frac{n}{2}),\ \cdots,\mathcal{A}_{nk-1}(nk-1) \Big\rangle,

where A0=⋯=Ank−n2−1\mathcal{A}_0=\cdots=\mathcal{A}_{nk-\frac{n}{2}-1} are nk−n2nk-\frac{n}{2} blocks of size (n/2k)\binom{n/2}{k}, and Ank−n2=⋯=Ank−1\mathcal{A}_{nk-\frac{n}{2}}=\cdots=\mathcal{A}_{nk-1} are n/2n/2 blocks of size (n/2−1k)\binom{n/2-1}{k}. Similarly, the dual Lefschetz decomposition of D~b(Pf(n−2k,V))\widetilde{D}^b({\mathrm {Pf}}(n-2k,V)) is

D~b(Pf(n−2k,V))=⟨Bn22−nk−1(−n22+nk+1), ⋯Bn(n−1)2−nk(−n(n−1)2+nk), Bn(n−1)2−nk−1(−n(n−1)2+nk+1), ⋯ ,B1(−1),B0⟩,\widetilde{D}^b({\mathrm {Pf}}(n-2k,V))=\Big\langle \mathcal{B}_{\frac{n^2}{2}-nk-1}(-\frac{n^2}{2}+nk+1),\ \cdots \mathcal{B}_{\frac{n(n-1)}{2}-nk}(-\frac{n(n-1)}{2}+nk),\ \mathcal{B}_{\frac{n(n-1)}{2}-nk-1}(-\frac{n(n-1)}{2}+nk+1),\ \cdots,\mathcal{B}_{1}(-1),\mathcal{B}_0\Big\rangle,

where B0=⋯=Bn(n−1)2−nk−1\mathcal{B}_0=\cdots=\mathcal{B}_{\frac{n(n-1)}{2}-nk-1} are n(n−1)2−nk\frac{n(n-1)}{2}-nk blocks of size (n/2n/2−k)\binom{n/2}{n/2-k}, and Bn(n−1)2−nk=⋯=Bn22−nk−1\mathcal{B}_{\frac{n(n-1)}{2}-nk}=\cdots=\mathcal{B}_{\frac{n^2}{2}-nk-1} are n/2n/2 blocks of size (n/2−1n/2−k)\binom{n/2-1}{n/2-k}. This predicts the Lefschetz structures required for Homological Projective Duality in the even-dimensional Pfaffian case, which remains open because the relevant categorical crepant resolutions and decompositions have not yet been constructed.

References

Primary source

Zengrui Han, “Stringy Hodge numbers of Pfaffian double mirrors and Homological Projective Duality”, arXiv:2409.17449 (2024).

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