The Fourier-Legendre series of Bessel functions of the first kind and the summed series involving $\,_{2}F_{3}$ hypergeometric functions that arise from them

Abstract

The Bessel function of the first kind $J_{N}\left(kx\right)$ is expanded in a Fourier-Legendre series, as is the modified Bessel functions of the first kind $I_{N}\left(kx\right)$. The purpose of these expansions in Legendre polynomials was not an attempt to rival established \emph{numerical methods} for calculating Bessel functions, but to provide a form for $J_{N}\left(kx\right)$ useful for \emph{analytical} work in the area of strong laser fields, where analytical integration over scattering angles is essential. Despite their primary purpose, we can easily truncate the series at 21 terms to provide 33-digit accuracy that matches IEEE extended precision in some compilers. The analytical theme is furthered by showing that infinite series of like-powered contributors (involving $\,_{2}F_{3}$ hypergeometric functions) extracted from the Fourier-Legendre series may be summed, having values that are inverse powers of the eight primes $1/\left(2^{i}3^{j}5^{k}7^{l}11^{m}13^{n}17^{o}19^{p}\right)$ multiplying powers of the coefficient $k$.