Quasi-modular forms from mixed Noether-Lefschetz theory

TL;DR

This paper extends the understanding of Gromov-Witten theory for K3 fibrations by introducing completed Noether-Lefschetz numbers for singular fibers, establishing quasi-modularity and holomorphic anomaly equations for related partition functions.

Contribution

It introduces completed Noether-Lefschetz numbers using toroidal compactifications to generalize Gromov-Witten theory results to singular fiber families.

Findings

Proved quasi-modularity for certain genus 0 partition functions.

Established holomorphic anomaly equations for these functions.

Extended Noether-Lefschetz theory to singular fiber cases.

Abstract

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.