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minor clarification; added 5 characters in body
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S. Carnahan
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If you view a $\mathbb{Z}$-valued (Cartier)Cartier divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacingif you replace the character group with a suitable fpqc sheaf of abelian groups on the base. This shows up for X a curve in some treatments of geometric class field theory, since the space of these divisors is the affine Grassmannian (in the sense of Beilinson-Drinfeld) for T over the Ran space of X. This space is used in, e.g., Gaitsgory's Twisted Whittaker model paper, where it forms a home (together with some similar objects) for factorizable sheaves.

If R is a number ring, you can demand that $X^\ast(T)$ be ana sheaf of R-modulemodules, so in this case, you're looking for torsors under tori with CM, with generic trivializations. I don't know where or if this is used, but it seems interesting enough.

If you view a $\mathbb{Z}$-valued (Cartier) divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacing the character group with a suitable fpqc sheaf of abelian groups on the base.

If R is a number ring, you can demand that $X^\ast(T)$ be an R-module, so in this case, you're looking for torsors under tori with CM, with generic trivializations. I don't know where or if this is used, but it seems interesting enough.

If you view a $\mathbb{Z}$-valued Cartier divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. The analogous construction will work for any group of multiplicative type, if you replace the character group with a suitable fpqc sheaf of abelian groups on the base. This shows up for X a curve in some treatments of geometric class field theory, since the space of these divisors is the affine Grassmannian (in the sense of Beilinson-Drinfeld) for T over the Ran space of X. This space is used in, e.g., Gaitsgory's Twisted Whittaker model paper, where it forms a home (together with some similar objects) for factorizable sheaves.

If R is a number ring, you can demand that $X^\ast(T)$ be a sheaf of R-modules, so in this case, you're looking for torsors under tori with CM, with generic trivializations. I don't know where or if this is used, but it seems interesting enough.

changed wording
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S. Carnahan
  • 45.7k
  • 6
  • 114
  • 220

If you view a $\mathbb{Z}$-valued (Cartier) divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacing the character group with a suitable fpqc sheaf of abelian groups on the base.

I don't know what you get if you want the action ofIf R is a largernumber ring -, you can certainly tensor up the character groups as abelian sheavesdemand that $X^\ast(T)$ be an R-module, so ifin this case, you're looking for torsors under tori with some kind of CM, I guess that will workwith generic trivializations. I don't know where or if this is used, but it seems interesting enough.

If you view a $\mathbb{Z}$-valued (Cartier) divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacing the character group with a suitable fpqc sheaf of abelian groups on the base.

I don't know what you get if you want the action of a larger ring - you can certainly tensor up the character groups as abelian sheaves, so if you're looking for tori with some kind of CM, I guess that will work.

If you view a $\mathbb{Z}$-valued (Cartier) divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacing the character group with a suitable fpqc sheaf of abelian groups on the base.

If R is a number ring, you can demand that $X^\ast(T)$ be an R-module, so in this case, you're looking for torsors under tori with CM, with generic trivializations. I don't know where or if this is used, but it seems interesting enough.

Source Link
S. Carnahan
  • 45.7k
  • 6
  • 114
  • 220

If you view a $\mathbb{Z}$-valued (Cartier) divisor (on say, an integral separated scheme X) as a $\mathbb{G}\_m$-torsor on X with generic trivialization, then for any torus T with character group $X^\ast(T)$, an $X^\ast(T)$-valued divisor on X is a T-torsor with generic trivialization. This shows up for X a curve, e.g., in some treatments of geometric class field theory and Gaitsgory's Twisted Whittaker model paper. The analogous construction will work for any group of multiplicative type, replacing the character group with a suitable fpqc sheaf of abelian groups on the base.

I don't know what you get if you want the action of a larger ring - you can certainly tensor up the character groups as abelian sheaves, so if you're looking for tori with some kind of CM, I guess that will work.