On the geometry of the Pappas-Rapoport models for PEL Shimura varieties

Abstract

We study integral models, so-called Pappas-Rapoport or splitting models, of some PEL Shimura Varieties whose data are ramified at a prime p. We show that except in a specific case, these models are smooth when there is no level at p, and we study their special fiber modulo p. We show that interesting stratifications appear, and we show that the $\mu$-ordinary locus is open and dense, following a strategy of Wedhorn in the unramified case.