Newton Polygons of Abelian $L$-Functions on Curves

Abstract: Let $X$ be a smooth, affine, geometrically connected curve over a finite field of characteristic $p > 2$. Let $\rho:\pi_1(X) \to \mathbb{C}^\times$ be a character of finite order $p^n$. If $\rho\neq 1$, then the Artin $L$-function $L(\rho,s)$ is a polynomial, and a theorem of Kramer-Miller states that its $p$-adic Newton polygon $\mathrm{NP}(\rho)$ is bounded below by a certain Hodge polygon $\mathrm{HP}(\rho)$ which is defined in terms of local monodromy invariants. In this talk we discuss the interaction between the polygons $\mathrm{NP}(\rho)$ and $\mathrm{HP}(\rho)$. Our main result states that if $X$ is ordinary, then $\mathrm{NP}(\rho)$ and $\mathrm{HP}(\rho)$ share a vertex if and only if there is a corresponding vertex shared by certain "local" Newton and Hodge polygons associated to each ramified point of $\rho$. As an application, we give a local criterion that is necessary and sufficient for $\mathrm{NP}(\rho)$ and $\mathrm{HP}(\rho)$ to coincide. This is joint work with Joe Kramer-Miller.

number theory

Audience: researchers in the topic

( paper )

Comments: pre-talk at 1:20pm

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UCSD number theory seminar

Series comments: Most talks are preceded by a pre-talk for graduate students and postdocs. The pre-talks start 40 minutes prior to the posted time (usually at 1:20pm Pacific) and last about 30 minutes.

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