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Ilya Nikokoshev
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How to make tensor category out of commutative algebraic groups?

Let's use the notation of [A=>B] for Hom(A, B). Take a 1-dimensional algebraic torus Gm and higher-dimensional torus T and let's live in the category of commutative algebraic groups over k.

Out of four expressions like [Gm => [Gm=>T]] etc. half give back T (*), others the dual torus TV, in the sense that X*(T) := [Gm => T] = [TV => Gm] =: X*(TV).

To prove equality (*) use for B = Gm

   (**)              A \otimes [B=>B] ==== [[A=>B] => B].

Question: Is there an example of commutative algebraic group B, other than Gm, for which the identity (**) is also true or perhaps true in some other sense?

(One thing I specifically have in mind is that if we could write [X => Y] = X* \otimes Y whenever X and Y are groups, as if it was a with any rigid tensor category, the formula would hold for all A and B)

Ilya Nikokoshev
  • 15.1k
  • 12
  • 77
  • 129