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Questions on group theory which concern finite groups.

34 votes
Accepted

Which groups have only real and quaternionic irreducible representations?

An irreducible representation is real or quaternionic precisely when its character is real-valued. By the Peter-Weyl theorem all characters are real-valued precisely when every element in the group is …
Torsten Ekedahl's user avatar
21 votes

Orbit structures of conjugacy class set and irreducible representation set under automorphis...

I think that an example of non-equivalent permutation sets is given by $G=(\mathbb Z/p\mathbb Z)^n$ for $n>2$ (and $p$ a prime). Then the automorphism group is $\mathrm{GL}_n(\mathbb Z/p\mathbb Z)$, t …
Torsten Ekedahl's user avatar
1 vote

A condition on finite groups

Such automorphisms appear naturally when one tries to analyse the group of automorphisms of $G$ preserving $H$ ($H$ may for instance be a characteristic subgroup so that it is preserved by all automor …
Torsten Ekedahl's user avatar