An Integral representation of $\mathop{\mathcal R}(s)$ due to Gabcke

Juan Arias de Reyna

Published 2024-07-01Version 1

Gabcke proved a new integral expression for the auxiliary Riemann function \[\mathop{\mathcal R}(s)=2^{s/2}\pi^{s/2}e^{\pi i(s-1)/4}\int_{-\frac12\searrow\frac12} \frac{e^{-\pi i u^2/2+\pi i u}}{2i\cos\pi u}U(s-\tfrac12,\sqrt{2\pi}e^{\pi i/4}u)\,du,\] where $U(\nu,z)$ is the usual parabolic cylinder function. We give a new, shorter proof, which avoids the use of the Mordell integral. And we write it in the form \begin{equation}\mathop{\mathcal R}(s)=-2^s \pi^{s/2}e^{\pi i s/4}\int_{-\infty}^\infty \frac{e^{-\pi x^2}H_{-s}(x\sqrt{\pi})}{1+e^{-2\pi\omega x}}\,dx.\end{equation} where $H_\nu(z)$ is the generalized Hermite polynomial.