1.II.19G
For a complex representation of a finite group , define the action of on the dual representation . If denotes the character of , compute the character of .
[Your formula should express just in terms of the character .]
Using your formula, how can you tell from the character whether a given representation is self-dual, that is, isomorphic to the dual representation?
Let be an irreducible representation of . Show that the trivial representation occurs as a summand of with multiplicity either 0 or 1 . Show that it occurs once if and only if is self-dual.
For a self-dual irreducible representation , show that either has a nondegenerate -invariant symmetric bilinear form or a nondegenerate -invariant alternating bilinear form, but not both.
If is an irreducible self-dual representation of odd dimension , show that the corresponding homomorphism is conjugate to a homomorphism into the orthogonal group . Here means the subgroup of that preserves a nondegenerate symmetric bilinear form on .