Decomposable Iitaka fibration conjecture

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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 B∈ΓB\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.

References

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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