Foliations in moduli spaces of abelian varieties and

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After my talk, in the evening of Friday 4-VIII-2000 Bjorn Poo- nen asked me ..... Consider minimal BT1 group schemes like Hd,c[p] as considered in Section 4.
Foliations in moduli spaces of abelian varieties and dimension of leaves Frans Oort

Version 26-V-2005

Felix-Klein-Kolloquium, D¨ usseldorf, 2 July 2005 Informal notes; not for publication

Introduction In this talk I consider moduli spaces of polarized abelian varieties in characteristic p. Also we consider deformation spaces of p-divisible groups. In these spaces we describe foliations, as constructed in [25]. What are the dimensions of leaves in these foliations, see (2.8)? We compute the dimensions of the central leaves, both in the unpolarized case and in the polarized case. These computations use either a result on “minimal p-divisible groups”, see [29], plus a result by Wedhorn, see [32], or a construction basically due to Ching-Li Chai which gives a generalization of Serre-Tate coordinates, see [2]. The dimension of a leaf in the unpolarized case, ζ = N (X), see (8.3): (r (((# ( ( ( (( # r ((ν2 (  # # dim(CX (D)) = 0