Arithmetic Wavefront Sets and Generic $L$-packets (2207.04700v2)

Abstract: Let $G$ be a classical group defined over a local field $F$ of characteristic zero. Let $\pi$ be an irreducible admissible representation $\pi$ of $G(F)$, which is of Casselman-Wallach type if $F$ is archimedean. If $\pi$ has a generic local $L$-parameter, we define the arithmetic wavefront set ${\rm WF_{ari}}(\pi)$ of $\pi$, which is a subset of $F$-rational nilpotent orbits of the Lie algebra $\mathfrak{g}(F)$ of $G(F)$, by means of the arithmetic structures of the enhanced $L$-parameter $(\varphi,\chi)$ of $\pi$. Those arithmetic structures are discovered by using our method of consecutive descents of enhanced $L$-parameters, based on the rationality of the local Langlands correspondence and the local Gan-Gross-Prasad conjecture. We study the basic structure of ${\rm WF_{ari}(\pi)}$ and prove that it is an invariant of $\pi$ (Theorem 5.10). The basic structures of ${\rm WF_{ari}(\pi)^{max}}$ are described by Conjecture 1.3, which asserts that the $F$-rational structure of ${\rm WF_{ari}(\pi)^{max}}$ can be completely determined by our method of consecutive descents of enhanced $L$-parameters. When $F$ is archimedean, Theorems 1.4 and 1.5 confirm much refined $F$-rational structure on ${\rm WF_{ari}(\pi)^{max}}$ than what Conjecture 1.3 says. Based on the local Langlands reciprocity, Conjecture 1.2 asserts that the wavefront sets on the $L$-parameter side should be closed related to those on the representation side, namely, [ {\rm WF_{wm}(\pi)^{max}}={\rm WF_{ari}(\pi)^{max}}={\rm WF_{tr}(\pi)^{max}} ] when $\pi$ has a generic local $L$-parameter, where the algebraic wavefront set ${\rm WF_{wm}}(\pi)$ is defined by Moeglin and Waldspurger [MW87] using generalized Whittaker models, and the analytic wavefront set ${\rm WF_{tr}}(\pi)$ is defined by Howe [H81, Hd85] using distribution characters, and also by [H74, HC78, BV80]. Conjecture 1.2 is verified for families of interesting cases.