On the prime-to-$p$ part of the groups of connected components of Néron models

Abstract

This article improves certain results of Dino Lorenzini concerning the groups of connected components of special fibres of Néron models of abelian varieties. Lorenzini has shown the existence of a four step filtration on the prime-to-$p$ part ($p$ is the residue characteristic), and proved certain bounds for the successive quotients. We improve these bounds and show that our bounds are sharp. As an application, we give a complete classification of the groups that can arise as the prime-to-$p$ part of the group of connected components of the Neron model of an abelian variety with given dimensions for the abelian, toric and unipotent part. Hard copies of this preprint are available.