The categorical crepant resolution conjecture for Pfaffian varieties

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(n2k,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), ,Ankn21(nkn21), Ankn2(nkn2), ,Ank1(nk1),\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==Ankn21\mathcal{A}_0=\cdots=\mathcal{A}_{nk-\frac{n}{2}-1} are nkn2nk-\frac{n}{2} blocks of size (n/2k)\binom{n/2}{k}, and Ankn2==Ank1\mathcal{A}_{nk-\frac{n}{2}}=\cdots=\mathcal{A}_{nk-1} are n/2n/2 blocks of size (n/21k)\binom{n/2-1}{k}. Similarly, the dual Lefschetz decomposition of D~b(Pf(n2k,V))\widetilde{D}^b({\mathrm {Pf}}(n-2k,V)) is

D~b(Pf(n2k,V))=Bn22nk1(n22+nk+1), Bn(n1)2nk(n(n1)2+nk), Bn(n1)2nk1(n(n1)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(n1)2nk1\mathcal{B}_0=\cdots=\mathcal{B}_{\frac{n(n-1)}{2}-nk-1} are n(n1)2nk\frac{n(n-1)}{2}-nk blocks of size (n/2n/2k)\binom{n/2}{n/2-k}, and Bn(n1)2nk==Bn22nk1\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/21n/2k)\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.

Sources & referencesView supporting material

Primary source

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

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