The generalized Kähler canonical bundle formula conjecture

Let f:XZf:X\to Z and ZSZ\to S be proper morphisms of normal relatively compact Kähler varieties such that fOX=OZf_*\mathcal O_X=\mathcal O_Z, and let (X/S,B+β)(X/S,B+\boldsymbol\beta) be a generalized pair. Suppose that

KX+B+βX=fγK_X+B+\boldsymbol\beta_X=f^*\gamma

for a ,\overline{\partial},\partial-closed current γ\gamma on ZZ. Let γ=γ\boldsymbol\gamma=\overline\gamma, define the boundary b-divisor BZ\mathbf B^Z and the moduli part βZ\boldsymbol\beta^Z by

βZ=γ(K+BZ),KZ+BZZ+βZZ=γZ.\boldsymbol\beta^Z=\boldsymbol\gamma-(\mathbf K+\mathbf B^Z),\qquad K_{Z'}+\mathbf B^Z_{Z'}+\boldsymbol\beta^Z_{Z'}=\boldsymbol\gamma_{Z'}.

Here BZ=BZZB_Z=\mathbf B^Z_Z on the given model.

Generalized Kähler canonical bundle formula conjecture. If f:(X,B+β)Zf:(X,B+\boldsymbol\beta)\to Z is a generalized klt (respectively, lc) pair as above, then (Z,BZ+βZ)(Z,B_Z+\boldsymbol\beta^Z) is a generalized klt (respectively, lc) pair.

This is the expected singularity statement in the canonical bundle formula for generalized Kähler pairs, analogous to the algebraic case. The source also expects the discriminant and moduli b-divisors to descend to a model and the moduli part to be nef, but those additional expectations are not part of the displayed conjecture. The resolution status is not specified in the source.

Sources & referencesView supporting material

Primary source

Christopher Hacon and Mihai Paun, “On the Canonical Bundle Formula and Adjunction for Generalized Kaehler Pairs”, arXiv:2404.12007 (2024).

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