Decomposable Iitaka fibration conjecture

Let dd be a positive integer and let Γ[0,1]\Gamma\subset[0,1] be a DCC set. A (Γ0,Γ)(\Gamma_0,\Gamma')-decomposable Iitaka fibration means that B=iaiBiB=\sum_i a_iB_i, where Γ0={a1,,ak}(0,1]\Gamma_0=\{a_1,\ldots,a_k\}\subset(0,1] is finite with iai=1\sum_i a_i=1, each BiB_i has coefficients in Γ\Gamma', each (X,Bi)(X,B_i) is lc, and every invariant Iitaka fibration of KX+BK_X+B is an Iitaka fibration of KX+BiK_X+B_i. The (m,Γ0,Γ)(m,\Gamma_0,\Gamma')-version additionally requires m(KX+Bi)|\lfloor m(K_X+B_i)\rfloor| to be birational to every invariant Iitaka fibration of KX+BK_X+B.

Decomposable Iitaka fibration conjecture. There exist a positive integer mm, a finite set Γ0(0,1]\Gamma_0\subset(0,1], and a DCC set Γ[0,1]\Gamma'\subset[0,1], depending only on dd and Γ\Gamma, such that every Q\mathbb Q-factorial lc pair (X,B)(X,B) of dimension dd with BΓB\in\Gamma and κι(X,KX+B)0\kappa_\iota(X,K_X+B)\ge0 has both a (Γ0,Γ)(\Gamma_0,\Gamma')-decomposable Iitaka fibration (weak version) and an (m,Γ0,Γ)(m,\Gamma_0,\Gamma')-decomposable Iitaka fibration (strong version).

This conjecture proposes a uniform perturbation of an invariant Iitaka fibration into an effective log Iitaka fibration and remains open.

Sources & referencesView supporting material

Primary source

Guodu Chen, Jingjun Han and Jihao Liu, “On effective log Iitaka fibrations and existence of complements”, arXiv:2301.04813 (2023).

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