Tuesday, 12 June 2007

rt.representation theory - How to make commutative algebraic groups strongly dualizable?

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).



The equality (*) can be proven by using the following formula with B = Gm



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



Question: Is there another example of commutative algebraic group or a similar generalized object B, for which the identity (**) is true or true in some generalized 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 they were vector spaces, the formula would hold for all A and B. So, what's a category that is related to algebraic groups but which posesses this property?

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