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Algebraic varieties with group operations given by morphisms, or group objects in the category of algebraic varieties, the category of algebraic schemes, or closely related categories.

22 votes
3 answers
6k views

The algebraic fundamental group of a reductive algebraic group

For a connected reductive algebraic group $G$ over a field $k$, other than the \'etale fundamental group of $G$ (regarded just as a scheme), there seems to be another notion, usually called the algebr …
shenghao's user avatar
  • 4,265
15 votes
Accepted

Is an algebraic space group always a scheme?

I think the answer is yes. If S is a noetherian scheme and G is a relative algebraic group space over S, then there is a stratification of S such that over each stratum, G is a group scheme (see K. Be …
shenghao's user avatar
  • 4,265
3 votes

How to topologize X(R) when R is a topological ring?

For adelic points of X (or G), one can first topologize X(Q_p) so that it becomes a p-adic analytic variety, and for almost all p one can define an open subset X(Z_p). Then take X(A) to be the restric …
shenghao's user avatar
  • 4,265
2 votes

algebraic group G vs. algebraic stack BG

Hello Ben, a little comment: when you say "G is a group scheme over k", you mean k is a separably closed field, right? Because otherwise the groupoid BG(k) may not have only one isomorphism class of …
shenghao's user avatar
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