The Gromov-Witten theory of threefolds admitting a smooth K3 fibration can be solved in terms of the Noether-Lefschetz intersection numbers of the fibration and the reduced invariants of a K3 surface. Toward a generalization of this result to families with singular fibers, we introduce completed Noether-Lefschetz numbers using toroidal compactifications of the period space of elliptic K3 surfaces. As an application, we prove quasi-modularity for some genus 0 partition functions of Weierstrass fibrations over ruled surfaces, and show that they satisfy a holomorphic anomaly equation.
Sketch of a programAn old approach to computing Gromov-Witten invariants on X is to embed ι : X ֒→ P as a complete intersection in a more positive variety P , often with a torus action. Composing with ι induces an embedding of Kontsevich spaces M g (X, β) ֒→ M g (P, ι * β).