Galois Actions on $\ell$-adic Local Systems and Their Nearby Cycles: A Geometrization of Fourier Eigendistributions on the $p$-adic Lie Algebra $\mathfrak{sl}(2)$

Abstract

In this thesis, two $\bar{\mathbb{Q}}_\ell$-local systems, $\vphantom{\mathcal{E}}^\circ \mathcal{E}$ and $\vphantom{E}^\circ \mathcal{E}^\prime$ on the regular unipotent subvariety $\mathcal{U}_{0,K}$ of $p$-adic $\operatorname{SL}_2(K)$ are constructed. Making use of the equivalence between $\bar{\mathbb{Q}}_\ell$-local systems and $\ell$-adic representations of the étale fundamental group, we prove that these local systems are equivariant with respect to conjugation by $\operatorname{SL}_2(K)$ and that their nearby cycles, when taken with respect to appropriate integral models, descend to local systems on the regular unipotent subvariety of $\operatorname{SL}_2(k)$, $k$ the residue field of $K$. Distributions on $\operatorname{SL}_2(K)$ are then associated to $\vphantom{E}^\circ \mathcal{E}$ and $\vphantom{E}^\circ \mathcal{E}^\prime$ and we prove properties of these distributions. Specifically, they are admissible distributions in the sense of Harish-Chandra and, after being transferred to the Lie algebra, are linearly independent eigendistributions of the Fourier transform. Together, this gives a geometrization of important admissible invariant distributions on a nonabelian $p$-adic group in the context of the Local Langlands program.