CM abelian schemes in mixed characteristic
-- Frans Oort, March 9, 2012

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Tate proved that any abelian variety defined over a
finite field is a CM abelian variety. Can it be CM lifted to
characteristic zero?  In joint work with Brian Conrad and
Ching-Li Chai we give a complete answer to various ways this
question can be phrased.  In my talk explicit examples and
general methods will be discussed, and some of the proofs will
be given.