Modular subvarieties of arithmetic quotients of bounded symmetric domains

Abstract

Arithmetic quotients are quotients of bounded symmetric domains by arithmetic groups, and modular subvarieties of arithmetic quotients are themselves arithmetic quotients of lower dimension which live on arithmetic quotients, by an embedding induced from an inclusion of groups of hermitian type. We show the existence of such modular subvarieties, drawing on earlier work of the author. If $\Gamma$ is a fixed arithmetic subgroup, maximal in some sense, then we introduce the notion of ``$\Gamma$-integral symmetric'' subgroups, which in turn defines a notion of ``integral modular subvarieties'', and we show that there are finitely many such on an (isotropic, i.e, non-compact) arithmetic variety.