Zeros of $E$-functions and of exponential polynomials defined over $\overline{\mathbb{Q}}$

Abstract

Zeros of Bessel functions $J_{\alpha }$ play an important role in physics. They are a motivation for studying zeros of exponential polynomials defined over $\overline{\mathbb{Q}}$, and more generally of $E$-functions. In this paper we partially characterize $E$-functions with zeros of the same multiplicity, and prove a special case of a conjecture of Jossen on entire quotients of $E$-functions, related to Ritt's theorem and Shapiro's conjecture on exponential polynomials. We also deduce from Schanuel's conjecture many results on zeros of exponential polynomials over $\overline{\mathbb{Q}}$, including $\pi$, logarithms of algebraic numbers, and zeros of $J_{\alpha }$ when $2\alpha$ is an odd integer. For the latter we define (if $\alpha \ne \pm 1/2$) an analogue of the minimal polynomial and Galois conjugates of algebraic numbers. At last, we study conjectural generalizations to factorization and zeros of $E$-functions.