Let V be an n-dimensional vector space, with n even, and let k be an integer. Write Pf(2k,V∨) and Pf(n−2k,V) for the corresponding Pfaffian varieties, and let Db denote their categorical crepant resolutions. A Lefschetz decomposition consists of admissible blocks Ai or Bi with the indicated twists.
Categorical crepant resolution conjecture. The categorical crepant resolution Db(Pf(2k,V∨)) has the non-rectangular Lefschetz decomposition
where A0=⋯=Ank−2n−1 are nk−2n blocks of size (kn/2), and Ank−2n=⋯=Ank−1 are n/2 blocks of size (kn/2−1). Similarly, the dual Lefschetz decomposition of Db(Pf(n−2k,V)) is
where B0=⋯=B2n(n−1)−nk−1 are 2n(n−1)−nk blocks of size (n/2−kn/2), and B2n(n−1)−nk=⋯=B2n2−nk−1 are n/2 blocks of size (n/2−kn/2−1). 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).