Prokhorov–Shokurov's effective b-semiampleness conjecture

Fix an integer dd. For every lc-trivial fibration f ⁣:XYf\colon X\to Y of relative dimension dd, choose a birational diagram

(X,Δ)ϕ(X,Δ)ffYψY.\begin{CD} (X',\Delta') @>{\phi}>> (X,\Delta)\\ @V{f'}VV @VV{f}V\\ Y' @>{\psi}>> Y. \end{CD}

Here ϕ\phi and ψ\psi are birational, and MY\mathbb M_{Y'} denotes the trace of the moduli b-divisor.

Effective b-semiampleness conjecture. There is an integer I=I(d)I=I(d) such that one can choose the diagram with KX+Δ=ϕ(KX+Δ)K_{X'}+\Delta'=\phi^*(K_X+\Delta), IMYI\mathbb M_{Y'} Cartier and free, and M{\bf M} descending to MY\mathbb M_{Y'}.

This is the effective, uniform form of the b-semiampleness expectation: the index depends only on the relative dimension. The conjecture is open in the stated generality.

Sources & referencesView supporting material

Primary source

Philip Engel, Stefano Filipazzi, François Greer, Mirko Mauri and Roberto Svaldi, “Boundedness of some fibered K-trivial varieties”, arXiv:2507.00973 (2025).

Additional references

8 papers in this index state this conjecture (2012–2025). The statement above is taken from the most recent of them; the others are arXiv:2405.05489, arXiv:2203.11460, arXiv:2111.03373, arXiv:2005.02613, arXiv:1907.10490, arXiv:1808.00717, arXiv:1207.4070.

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