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arxiv: 1812.04208 · v1 · pith:3Y4QZCDUnew · submitted 2018-12-11 · 🧮 math.NT · math.RT

Change of coefficients in the p neq ell local Langlands correspondence for GL_n

classification 🧮 math.NT math.RT
keywords localcorrespondencegaloislanglandscharacteristiccoefficientstildealgebras
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Let $\ell$ and $p$ be distinct primes, $n$ a positive integer, $F_\ell$ an $\ell$-adic local field of characteristic $0,$ and let $W(k)$ denote the ring of Witt vectors over an algebraically closed field of characteristic $p$. Work of Emerton-Helm, Helm and Helm-Moss defines and constructs a smooth $A[{GL}_n(F_\ell)]$-module $\tilde{\pi}(\rho_A)$ for a continuous Galois representation $\rho_A : G_{F_\ell} \to {GL}_n(A)$ over a $p$-torsionfree reduced complete local $W(k)$-algebra $A$ interpolating the local Langlands correspondence. However, since $\tilde{\pi}$ is not a functor, there is no clear way to speak about the local Langlands correspondence over non-reduced or finite characteristic $W(k)$-algebras. We describe two natural and reasonable variants of the local Langlands correspondence with arbitrary complete local $W(k)$-algebras as coefficients. They are isomorphic when evaluated on the universal framed deformation of a Galois representation $\overline{\rho}$ over $k$, and more generally we find a surjection in one direction. In many cases, including $n=2$ or $3,$ they both recover $\tilde{\pi}(\rho)$ when $\rho$ has coefficients in a finite extension of $W(k)[p^{-1}].$ On the Galois side, this requires finding minimal lifts between Galois deformations.

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