Michel Brion
Published 2013-10-01, updated 2013-12-21Version 2
We show that every connected commutative algebraic group over an algebraically closed field of characteristic 0 is the Picard variety of some projective variety, obtained by pinching a smooth variety along a finite subscheme. In contrast, no Witt group of dimension at least 3 over a perfect field of prime characteristic is isogenous to the Picard variety obtained by this construction.
Comments: Statement and proof of Theorem 2 corrected
Saturation bounds for smooth varieties
The deformation theory of representations of the fundamental group of a smooth variety
On the center of the ring of differential operators on a smooth variety over $\bZ/p^n\bZ$
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