Cuspidal representations which are not strongly cuspidal

Abstract

We give a description of all the cuspidal representations of ${\mathrm{GL}}_4({\mathfrak{o}}_2)$, where ${\mathfrak{o}}_2$ is a finite ring coming from the ring of integers in a local field, modulo the square of its maximal ideal $\mathfrak{p}$. This shows in particular the existence of representations which are cuspidal, yet are not strongly cuspidal, that is, do not have orbit with irreducible characteristic polynomial mod $\mathfrak{p}$. It has been shown by Aubert, Onn, and Prasad that this phenomenon cannot occur for ${\mathrm{GL}}_n$, when $n$ is prime.

5 pages