Character Theory for Semilinear Representations

Abstract

Let $G$ be a group acting on a field $L$, and suppose that $L/L^G$ is a finite extension. We show that the category of semilinear representations of $G$ over $L$ can be described in terms of the category of linear representations of $H$, the kernel of the map $G\to \mathrm{Aut}(L)$. When $G$ is finite and $L$ has characteristic 0 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.

v3: minor improvements, including extension from irreducible to indecomposable representations