Additive extensions of a Barsotti-Tate group

Abstract

In this paper we classify up to isomorphism the additive extensions of a Barsotti-Tate group, in positive characteristic p over a perfect field k and in characteristic 0 over W(k) the ring of Witt vectors with coefficients in k. The extensions arise as group functors associated to suitable submodules of the Dieudonné module. In particular we give an explicit description of the universal additive extension in both cases.

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