Asymptotic expoansions of mathieu-Bessel series. I (1907.01812v2)

Abstract: We consider the asymptotic expansion of the Mathieu-Bessel series [S_\nu(a,b)=\sum_{n=1}^\infty \frac{n^\gamma J_\nu(nb/a)}{(n^2+a^2)^\mu}, \qquad (\mu, b>0,\ \gamma, \nu\in {\bf R})] as $a\to+\infty$ with the other parameters held fixed, where $J_\nu(x)$ is the Bessel function of the first kind of order $\nu$. A special case arises when $\gamma+\nu$ is a positive even integer, where the expansion comprises finite algebraic terms together with an exponentially small expansion. Numerical examples are presented to illustrate the accuracy of the various expansions. The expansion of the alternating variant of $S_\nu(a,b)$ is considered. The series when the $J_\nu(x)$ function is replaced by the Bessel function $Y_\nu(x)$ is briefly mentioned.