The nef-cone conjecture for codimension-two classes on the compactification of A_3

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Let A3‾\overline{{\mathcal A}_{3}} be the toroidal compactification, and let LL, MM, and β2\beta_2 be the classes used in the paper. Define

F1=−72L2+12LM+3M2+β2,F2=72L2−8LM+M2−β2.F_1=-72L^2+12LM+3M^2+\beta_2,\qquad F_2=72L^2-8LM+M^2-\beta_2.

Nef-cone conjecture. The cone of nef codimension-two classes is

Nef⁡2(A3‾)=R≥0L2+R≥0LM+R≥0M2+R≥0F1+R≥0F2.\operatorname{Nef}^{2}(\overline{{\mathcal A}_{3}})={\mathbb R}_{\ge 0}L^2+{\mathbb R}_{\ge 0}LM+{\mathbb R}_{\ge 0}M^2+{\mathbb R}_{\ge 0}F_1+{\mathbb R}_{\ge 0}F_2.

The source states that this is equivalent to the main effective-cone conjecture; it remains unresolved because generation of the pseudoeffective cone by the five surfaces has not been proved.

References

Primary source

Samuel Grushevsky and Klaus Hulek, “On the cone of effective surfaces on A_3”, arXiv:2007.02995 (2022).

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