Phenomenological fits to low-energy $\pi$-nucleus scattering have uniformly required a greatly enhanced $s$-wave repulsion in the optical potential, for which no satisfactory theoretical explanation has been given. Evaluation of nonlinear terms in field-theoretic Lagrangians with broken chiral symmetry and inclusion of necessary binding effects leads to a substantial, repulsive ${\rho }^2\mathrm{}\left(r\right)\mathrm{}$ potential, even on an isospin zero target. This potential may account for the previously unexplained effect.

NUCLEAR REACTIONS Pion-nucleus elastic scattering; field theoretic optical potential. Binding corrections. ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ targets.

• Received 5 October 1979

DOI:https://doi.org/10.1103/PhysRevC.22.1211