Number of Kummer structures and Moduli spaces of generalized Kummer surfaces

TL;DR

This paper investigates the classification and number of Kummer structures on generalized Kummer surfaces, linking algebraic cases to Shimura curves and exploring quaternion orders in complex tori.

Contribution

It provides a classification of moduli spaces of generalized Kummer surfaces and relates the number of Kummer structures to Shimura curves and quaternion orders.

Findings

Number of Kummer structures can be powers of two for certain surfaces.

In algebraic cases, Kummer structures relate to order 3 elliptic points on Shimura curves.

Non-algebraic surfaces have a unique Kummer structure but complex moduli space components.

Abstract

A generalized Kummer surface $X=Km_{3}(A,G_{A})$ is the minimal resolution of the quotient of a $2$-dimensional complex torus by an order 3 symplectic automorphism group $G_{A}$. A Kummer structure on $X$ is an isomorphism class of pairs $(B,G_{B})$ such that $X\simeq Km_{3}(B,G_{B})$. When the surface is algebraic, we obtain that the number of Kummer structures is linked with the number of order $3$ elliptic points on some Shimura curve naturally related to $A$. For each $n\in\mathbb{N}$, we obtain generalized Kummer surfaces $X_{n}$ for which the number of Kummer structures is $2^{n}$. We then give a classification of the moduli spaces of generalized Kummer surfaces. When the surface is non algebraic, there is only one Kummer structure, but the number of irreducible components of the moduli spaces of such surfaces is large compared to the algebraic case. The endomorphism rings of the complex $2$-tori we study are mainly quaternion orders, these order contain the ring of Eisenstein integers. One can also see this paper as a study of quaternion orders $\mathcal{O}$ over $\mathbb{Q}$ that contain the ring of Eisenstein integers. We obtain that such order is determined up to isomorphism by its discriminant, and when the quaternion algebra is indefinite, the order $\mathcal{O}$ is principal.