Families of abelian varieties with many isogenous fibres

TL;DR

This paper proves that a one-dimensional subvariety of the moduli space of principally polarised abelian varieties containing a dense set of isogenous varieties is weakly special, extending previous results to a broader context.

Contribution

It generalizes the André-Pink conjecture for one-dimensional subvarieties with dense isogeny classes using the Pila–Zannier method and the Masser–Wüstholz theorem.

Findings

Proves the André-Pink conjecture for dim Z=1 with dense isogeny classes.

Extends previous results to non-CM and non-Galois generic points.

Utilizes Pila–Zannier method and isogeny theorems for the proof.

Abstract

Let Z be a subvariety of the moduli space of principally polarised abelian varieties of dimension g over the complex numbers. Suppose that Z contains a Zariski dense set of points which correspond to abelian varieties from a single isogeny class. A generalisation of a conjecture of Andr\'e and Pink predicts that Z is a weakly special subvariety. We prove this when dim Z = 1 using the Pila--Zannier method and the Masser--W\"ustholz isogeny theorem. This generalises results of Edixhoven and Yafaev when the Hecke orbit consists of CM points and of Pink when it consists of Galois generic points.