Effective characterization of semi-abelian varieties

Let d≥1d \geq 1 be an integer. For a smooth complex variety VV of dimension dd, let q‾(V)\overline{q}(V) denote its logarithmic irregularity, let P‾m(V)\overline{P}_m(V) denote its mm-th logarithmic plurigenus, and let aV ⁣:V→A(V)a_V \colon V \to A(V) be its Albanese morphism to the universal semi-abelian variety.

Effective semi-abelian characterization conjecture. There exists an integer k=k(d)≥1k = k(d) \geq 1 such that, whenever

q‾(V)=dim⁡(V)andP‾1(V)=⋯=P‾k(V)=1,\overline{q}(V) = \dim(V) \quad\text{and}\quad \overline{P}_1(V) = \dots = \overline{P}_k(V) = 1,

then aV ⁣:V→A(V)a_V \colon V \to A(V) is an isomorphism away from a closed subset of A(V)A(V) of codimension at least 22.

This conjecture seeks an effective quasi-projective analogue of the Chen–Hacon characterization of varieties birational to abelian varieties, replacing projective irregularity and plurigenera by logarithmic invariants and describing the resulting semi-abelian Albanese morphism in codimension one. The supplied source gives no evidence of resolution.

References

Primary source

Jefferson Baudin and Sofia Tirabassi, “Effective characterization of semi-abelian varieties”, arXiv:2607.20296 (2026).

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