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math.AG2025
Extensions Of Unirational Groups
Zev Rosengarten
We undertake a study of extensions of unirational algebraic groups. We prove that extensions of unirational groups are also unirational over fields of degree of imperfection , b…
math.AG2025
Extensions of Abelian Schemes and the Additive Group
Gabriel Ribeiro, Zev Rosengarten
We compute extension sheaves of abelian schemes and of the additive group by the multiplicative group in the fppf topology. Our main results include a generalized and streamlined p…
math.AG2022
Picard Groups Of Algebraic Groups And An Affineness Criterion
Zev Rosengarten
We prove that an algebraic group over a field is affine precisely when its Picard group is torsion, and show that in this case the Picard group is finite when is perfect, an…