Matrices of simple spectrum in irreducible representations of cyclic extensions of simple algebraic groups

Abstract

Let $H$ be a linear algebraic group whose connected component $G\neq 1$ is simple and $H/G$ is cyclic. We determine the irreducible projective representations $\phi$ of $H$ such that $\phi(G)$ is irreducible and $\phi(h)$ has simple spectrum for some $h\in H$. The latter means that all irreducible constituents of the group $\phi( \langle h\rangle)$ are of multiplicity 1. (Here $\langle h\rangle$ is the subgroup of $H$ generated by $h$.) This extends an earlier known result for $H=G$.