Timeline for Is the normalizer of a reductive subgroup reductive?
Current License: CC BY-SA 3.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 27, 2012 at 10:54 | vote | accept | Martin Orr | ||
| Nov 25, 2012 at 13:40 | answer | added | George McNinch | timeline score: 14 | |
| Nov 24, 2012 at 22:38 | comment | added | user27056 | @Ben Wieland: I imposed a connectedness condition in my answer because it seemed almost certain that Martin Orr would have wanted that ("everything" breaks down in the theory of linear algebraic groups when one drops connectedness). One should never say "reductive" without connectedness in positive characteristic, since too many things break down in such cases. | |
| Nov 24, 2012 at 20:34 | comment | added | Ben Wieland | Positive characteristic: I don't think anyone spelled this out: for a finite group, the normalizer need not be reductive. EG, for $\mathbb Z/p$ acting by shearing on a 2d vector space, the connected component of the normalizer is $\mathbb G_a$.....This is what xbnv asks for: a nontrivial extension of a rep by itself. But the standard examples of nontrivial extensions of $SL_2$-reps have distinct composition factors, so I don't know. | |
| Nov 23, 2012 at 23:02 | answer | added | user27056 | timeline score: 19 | |
| Nov 23, 2012 at 22:41 | answer | added | Jim Humphreys | timeline score: 7 | |
| Nov 23, 2012 at 15:02 | answer | added | Venkataramana | timeline score: 17 | |
| Nov 23, 2012 at 14:38 | history | asked | Martin Orr | CC BY-SA 3.0 |