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For questions about modular representation theory, the study of representations over a field of positive characteristic.

1 vote

Reference for fact about reduction mod $p$ of a representation of a finite group

I don't know of just a citation, but here is a pretty quick way to deduce this from the literature (I imagine that this might be the argument you had in mind, in which case apologies for telling you t …
Alex B.'s user avatar
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6 votes
Accepted

Irreducible mod-p representation of a semidirect product with trivial p-core

The following is a direct proof that any extension of $G$ by $V$ splits. It is taken from a joint paper of mine with Tim Dokchitser, where the proof starts in the last paragraph of page 12. First, no …
Alex B.'s user avatar
  • 13k
7 votes
Accepted

Defect groups and subgroups

This is an exercise in writing out the definitions: since the defect group of $B$ is $E$, we have $B|(B_{\delta(E)})^{G\times G}$. So by assumption, $$ b\;|\;B_{H\times H}\;|\;\left((B_{\delta(E)})^{G …
Alex B.'s user avatar
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