Paper 2, Section II, 15F15 F

Representation Theory
Part II, 2015

Let GG be a finite group. Suppose that ρ:GGG(V)\rho: G \rightarrow G \mathrm{G}(V) is a finite-dimensional complex representation of dimension dd. Let nNn \in \mathbb{N} be arbitrary.

(i) Define the nnth symmetric power SnVS^{n} V and the nnth exterior power ΛnV\Lambda^{n} V and write down their respective dimensions.

Let gGg \in G and let λ1,,λd\lambda_{1}, \ldots, \lambda_{d} be the eigenvalues of gg on VV. What are the eigenvalues of gg on SnVS^{n} V and on ΛnV\Lambda^{n} V ?

(ii) Let XX be an indeterminate. For any gGg \in G, define the characteristic polynomial Q=Q(g,X)Q=Q(g, X) of gg on VV by Q(g,X):=det(gXI)Q(g, X):=\operatorname{det}(g-X I). What is the relationship between the coefficients of QQ and the character χΛnV\chi_{\Lambda^{n}} V of the exterior power?

Find a relation between the character χSnV\chi_{S^{n}} V of the symmetric power and the polynomial QQ.