Constructing local L-packets for tame unitary groups

Abstract

We generalize the work of DeBacker and Reeder to the case of unitary groups split by a tame extension. The approach is broadly similar and the restrictions on the parameter the same, but many of the details of the arguments differ. Let $G$ be a unitary group defined over a local field $K$ and splitting over a tame extension $E/K$. Given a Langlands parameter $\varphi : \mathcal{W}_K \rightarrow {^L G}$ that is tame, discrete and regular, we give a natural construction of an $L$-packet $\Pi_\varphi$ associated to $\varphi$, consisting of representations of pure inner forms of $G(K)$ and parametrized by the characters of the finite abelian group $A_\varphi = \operatorname{Z}_{\hat{G}}(\varphi)$.