Field theoretic treatment ofπ-nuclear scattering

The dynamical assumption that single mesons are emitted or absorbed by nucleons is applied to $\pi$-nucleus scattering and leads to a $\pi$-nucleus Low equation. With the neglect of multinucleon currents and true meson absorption, the $\pi$-nucleus Low equation is shown to be equivalent to a linear equation of the same form as in standard theories except for a striking propagator modification arising from the energy dependence of the driving term. The use of a corresponding linear equation for $\pi$-nucleon scattering enables us to derive a field-theoretic multiple-scattering series. It is found that the propagator modification eliminates the Kisslinger singularity, reduces the Lorentz-Lorenz effect and local field corrections. The effect of true meson absorption on $\pi$-nucleus elastic scattering is also examined and found to be somewhat important at low (∼50 MeV) energies but negligible (due to strong first-order optical absorption) for energies greater than 100 MeV.