Zeros of the Goss zeta function

Abstract

Let $X$ be a smooth proper curve over a finite field and let $\infty \in X$ be a closed point. Let $A$ be the ring of functions on $X - \infty$. The Goss zeta function $\zeta_A$ of $A$ is an equicharacteristic analogue of the Riemann zeta function. In this article we study the zeros of $\zeta_A$ under the generic condition that $X$ is ordinary. We prove an analogue of the Riemann hypothesis, which verifies a corrected version of a conjecture of Goss. We also show that the zeros of $\zeta_A$ at negative even integers are `simple' and that $\zeta_A$ is nonzero at negative odd integers. This answers questions posed by Goss and Thakur. Both of these results were previously only known under the restrictive hypothesis that $A$ has class number one. Finally, we prove versions of these results for $v$-adic interpolations of the Goss zeta function.