Contributions of nucleon momenta to the pion optical potential

The pion-nucleus scattering amplitude in the impulse approximation is expressed in terms of the invariant matrix for pion-nucleon scattering. It is pointed out that the linear nucleon momentum terms evaluated in the nuclear ground state constitute a longitudinal current that is nonzero. It is shown that these terms reduce by a factor of $\frac{1}{2}$ the ${\Delta }^2\rho \left(\overrightarrow{\mathrm{r}}\right)$ addition to the optical potential obtained by Kisslinger and Tabakin.