Paper 1, Section II, H

Representation Theory
Part II, 2014

(i) Let KK be any field and let λK\lambda \in K. Let Jλ,nJ_{\lambda, n} be the n×nn \times n Jordan block

Jλ,n=(λ10000100λ)J_{\lambda, n}=\left(\begin{array}{ccccc} \lambda & 1 & 0 & \cdots & 0 \\ 0 & \ddots & \ddots & & \vdots \\ \vdots & & \ddots & \ddots & 0 \\ \vdots & & & \ddots & 1 \\ 0 & \cdots & \cdots & 0 & \lambda \end{array}\right)

Compute Jλ,nrJ_{\lambda, n}^{r} for each r0r \geqslant 0.

(ii) Let GG be a cyclic group of order NN, and let KK be an algebraically closed field of characteristic p0p \geqslant 0. Determine all the representations of GG on vector spaces over KK, up to equivalence. Which are irreducible? Which do not split as a direct sum WWW \oplus W^{\prime}, with W0W \neq 0 and W0?W^{\prime} \neq 0 ?