Monday, Jan 26

Speaker: Marc-Hubert Nicole (Jussieu)

Title: Purity of level m stratifications

Abstract: We will discuss stratifications coming from truncations of Barsotti-Tate groups (also called p-divisible groups), generalizing the Ekedahl-Oort stratification. After recalling some background material, we will explain the hierarchy of purity properties, and describe in detail the situation for some classical stratifications. We will illustrate the main result in the case of the Siegel modular varieties, and mention briefly how our techniques apply to good reductions of Shimura varieties of Hodge type. Joint work with A. Vasiu and T. Wedhorn.