A Torelli theorem for osculating cones to the theta divisor
Si dà una nuova e completa dimostrazione del risultato cruciale del metodo di Ruppert che consente di stabilire in maniera effettiva quando una superficie abeliana è isomorfa o isogena a un prodotto di curve ellittiche.
The aim of this paper is to extend our previous results about Galois action on the torsion points of abelian varieties to the case of (finitely generated) fields of characteristic 2.
We estimate the fraction of isogeny classes of abelian varieties over a finite field which have a given characteristic polynomial modulo . As an application we find the proportion of isogeny classes of abelian varieties with a rational point of order .