Weak Analytic Geometry and a Trace Formula for Families of $p$-adic Representations

Abstract

The eigencurve is a powerful tool introduced by Coleman and Mazur to study $p$-adic families of overconvergent modular forms. In this article, we introduce an analogous set of tools for understanding families of "overconvergent" $p$-adic representations of $\pi_1(X)$, where $X$ is a smooth affine variety over a finite field of characteristic $p$. Our main theorem is a trace formula relating the $L$-function of such a family to the geometry of a sequence of associated eigenvarieties. In the case of a single $p$-adic representation, our result reduces to the well known trace formula of Monsky. We apply our theory to the study of $T$-adic exponential sums attached to $\mathbb{Z}_p$-towers over $X$. Special cases of this theory have been applied by Davis, Wan, and Xiao to prove a spectral halo decomposition of the eigencurve attached to $\mathbb{Z}_p$-towers over $X=\mathbb{A}^1$.