Normal Forms, K3 Surface Moduli, and Modular Parametrizations

TL;DR

This paper studies special K3 surfaces with a specific polarization, deriving differential equations for their periods, exploring subloci with enhanced polarization, and relating findings to Moonshine groups and elliptic curves.

Contribution

It provides an explicit normal form for these K3 surfaces, derives Picard-Fuchs equations, and links polarization enhancements to Moonshine group quotients.

Findings

Derived Picard-Fuchs equations for K3 surface periods

Identified subloci with enhanced polarization and their differential equations

Connected polarization subloci to genus zero Moonshine group quotients

Abstract

The geometric objects of study in this paper are K3 surfaces which admit a polarization by the unique even unimodular lattice of signature (1,17). A standard Hodge-theoretic observation about this special class of K3 surfaces is that their polarized Hodge structures are identical with the polarized Hodge structures of abelian surfaces that are cartesian products of elliptic curves. Earlier work of the first two authors gives an explicit normal form and construction of the moduli space for these surfaces. In the present work, this normal form is used to derive Picard-Fuchs differential equations satisfied by periods of these surfaces. We also investigate the subloci of the moduli space on which the polarization is enhanced. In these cases, we derive information about the Picard-Fuchs differential equations satisfied by periods of these subfamilies, and we relate this information to the theory of genus zero quotients of the upper half-plane by Moonshine groups. For comparison, we also examine the analogous theory for elliptic curves in Weierstrass form.