Character Theory for Semilinear Representations

Abstract: Let $G$ be a group acting on a field $L$, and suppose that $L /K$ is a finite Galois extension, where $K = L^G$. We show that the irreducible semilinear representations of $G$ over $L$ can be completely described in terms of irreducible linear representations of $H$, the kernel of $G \rightarrow \mathrm{Gal}(L/K)$. When $G$ is finite and $|G| \in L^{\times}$ this provides a character theory for semilinear representations of $G$ over $L$, which recovers ordinary character theory when the action of $G$ on $L$ is trivial.