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4 votes
0 answers
77 views

Conjugacy of cocharacters from conjugacy of labelled diagrams

Everything to follow is over some fixed algebraically closed field $k$. Although all the definitions make sense regardless of characteristic, the meat of the question is about small positive ...
3 votes
1 answer
245 views

Can non-geometrically reduced reduced subschemes happen for reductive groups?

The title is meant to be punchy, but also a tongue-in-cheek acknowledgement of the prevalence of ‘reduce’-derived words in this area. (Unfortunately, I overlooked the fact that the question in the ...
5 votes
1 answer
419 views

Lifting $\mathfrak{sl}_2$-triples

Let $k$ be an algebraically closed field, $G$ a (smooth, connected) reductive algebraic group over $k$, $H$ a (smooth, connected) reductive group of semisimple rank 1, and $T$ a maximal torus in $H$. ...
9 votes
1 answer
545 views

Showing subgroups with equal Lie algebras are equal

Let $k$ be a field. It might as well be algebraically closed, but I do not want to assume that it has characteristic $0$. I will write "group" for "affine group scheme over $k$", ...