Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2026/iii/paper-102/1/ii/solution
Let represent . Since is central, commutes with and . Over the complex number field , has an eigenvalue , and its corresponding eigenspace is invariant under all three operators. The irreducibility of therefore makes this eigenspace all of , so . Taking the trace ofgives by the cyclic property of the trace; hence .
The remaining operators and commute. Two commuting operators on a nonzero finite-dimensional complex vector space have a common eigenvector, whose span is invariant. Irreducibility therefore forces . Conversely, every pair defines a one-dimensional irreducible representation byThese are all the finite-dimensional irreducible representations.
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