S-wave $\pi$-Nucleus Repulsion and Dirac Phenomenology

A relativistic $\pi$-nucleon potential is extended to $m^* \neq m$ to investigate the possibility of generating s-wave $\pi$-nucleus repulsion. We find that relativity does indeed generate significant repulsion, the exact amount depending on the details of the calculation. In contradistinction the $t\rho$ approximation gives very little repulsion.