Curves on K3 surfaces in divisibility two

Abstract

We prove a conjecture of Maulik, Pandharipande, and Thomas expressing the Gromov--Witten invariants of K3 surfaces for divisibility two curve classes in all genus in terms of weakly holomorphic quasimodular forms of level two. Then, we establish the holomorphic anomaly equation in divisibility two in all genus. Our approach involves a refined boundary induction, relying on the top tautological group of the moduli space of smooth curves, together with a degeneration formula for reduced virtual fundamental class with imprimitive curve classes. We use the double ramification relations with target variety as a new tool to prove the initial condition. The relationship between the holomorphic anomaly equation for higher divisibility and the conjectural multiple cover formula of Oberdieck and Pandharipande is discussed in detail and illustrated with several examples.

arXiv comment48 pages, Forum of Mathematics, Sigma (to appear)

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• Double ramification cycles on the moduli spaces of curves
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• Holomorphic anomaly equations and the Igusa cusp form conjecture
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• Top tautological group of ${\mathcal{M}}_{g,n}$

Cited by in corpus (2)

• Multiple cover formulas for K3 geometries, wall-crossing, and Quot schemes
• Holomorphic anomaly equations for the Hilbert scheme of points of a K3 surface