Generalized Ambro conjecture for weak log Fano pairs

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Let (Y,B)(Y,B) be an ϵ\epsilon-klt weak log Fano pair of dimension nn with YY having at worst terminal singularities. For a Q\mathbb{Q}-Cartier divisor GG satisfying G+B≥0G+B\geq0, define

glct(Y,B;G)=sup⁡{t∈[0,1]∩Q∣(Y,B+tG) is lc}.{\rm glct}(Y,B;G)=\sup\{t\in[0,1]\cap\mathbb{Q}\mid (Y,B+tG)\text{ is lc}\}.

Generalized Ambro conjecture. Fix 0<ϵ<10<\epsilon<1 and an integer n>0n>0. Then there exists a number μ(n,ϵ)>0\mu(n,\epsilon)>0 depending only on nn and ϵ\epsilon such that

inf⁡{glct(Y,B;G)∣G∼Q−(KY+B), G+B≥0}≥μ(n,ϵ).\inf\{ {\rm glct}(Y,B;G)\mid G\sim_\mathbb{Q}-(K_Y+B),\ G+B\geq0\}\geq\mu(n,\epsilon).

This stronger formulation allows GG to be non-effective, subject to G+B≥0G+B\geq0, and is needed for the paper's argument. The supplied text gives no resolution status, so it is recorded as open with low confidence.

References

Primary source

Chen Jiang, “Boundedness of anti-canonical volumes of singular log Fano threefolds”, arXiv:1411.6728 (2017).

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