Local Langlands correspondence for $GL_n$ and the exterior and symmetric square $\varepsilon$--factors

TL;DR

This paper proves that the local Langlands correspondence preserves symmetric and exterior square epsilon factors for $GL_n$ over $p$-adic fields, using deformation and local/global techniques to establish stability under ramified twists.

Contribution

It demonstrates the compatibility of the local Langlands correspondence with symmetric and exterior square epsilon factors, extending the robustness of the correspondence.

Findings

Epsilon factors are preserved under the correspondence.

Stability of gamma-factors under ramified twists is established.

The approach combines deformation, local/global methods, and asymptotic analysis of Bessel functions.

Abstract

Let $F$ be a $p$--adic field, i.e., a finite extension of $\mathbb Q_p$ for some prime $p$. The local Langlands correspondence attaches to each continuous $n$--dimensional $\Phi$-semisimple representation $\rho$ of $W'_F$, the Weil--Deligne group for $\bar F/F$, an irreducible admissible representation $\pi(\rho)$ of $GL_n(F)$ such that, among other things, the local $L$- and $\varepsilon$-factors of pairs are preserved. This correspondence should be robust and preserve various parallel operations on the arithmetic and analytic sides, such as taking the exterior square or symmetric square. In this paper, we show that this is the case for the local arithmetic and analytic symmetric square and exterior square $\varepsilon$--factors, that is, that $\varepsilon(s,\Lambda^2\rho,\psi)=\varepsilon(s,\pi(\rho),\Lambda^2,\psi)$ and $\varepsilon(s,Sym^2\rho,\psi)=\varepsilon(s,\pi(\rho),Sym^2,\psi)$. The agreement of the $L$-functions also follows by our methods, but this was already known by Henniart. The proof is a robust deformation argument, combined with local/global techniques, which reduces the problem to the stability of the analytic $\gamma$-factor $\gamma(s,\pi,\Lambda^2,\psi)$ under highly ramified twists when $\pi$ is supercuspidal. This last step is achieved by relating the $\gamma$-factor to a Mellin transform of a partial Bessel function attached to the representation and then analyzing the asymptotics of the partial Bessel function, inspired in part by the theory of Shalika germs for Bessel integrals. The stability for every irreducible admissible representation $\pi$ then follows from those of the corresponding arithmetic $\gamma$--factors as a corollary.