Computing Igusa's local zeta function of univariates in deterministic polynomial-time

Abstract

Igusa's local zeta function $Z_{f,p}(s)$ is the generating function that counts the number of integral roots, $N_k(f)$, of $f(\mathbf{x})\mathrm{mod}{p}^k$, for all $k$. It is a famous result, in analytic number theory, that $Z_{f,p}$ is a rational function in $\mathbb{Q}(p^s)$. We give an elementary proof of this fact for a univariate polynomial $f$. Our proof is constructive as it gives a closed-form expression for the number of roots $N_k(f)$. Our proof, when combined with the recent root-counting algorithm of (Dwivedi, Mittal, Saxena, CCC, 2019), yields the first deterministic poly($|f|,\log p$) time algorithm to compute $Z_{f,p}(s)$. Previously, an algorithm was known only in the case when $f$ completely splits over ${\mathbb{Q}}_p$; it required the rational roots to use the concept of generating function of a tree (Zúñiga-Galindo, J.Int.Seq., 2003).

15 pages, ANTS 2020