Parity-violating nucleon-pion interaction and simultaneous fits to nonleptonic hyperon decays

The parity-violating NNπ amplitude is usually determined through SU(3) sum rules relating strangeness-conserving to strangeness-changing decay amplitudes. Examination of recent simultaneous fits to strangeness-changing s- and p-wave amplitudes employing pole terms reveals that the NNπ amplitude is reduced by a factor of 3 relative to earlier sum-rule fits. Pole terms also provide a basis for extrapolation to off-mass-shell amplitudes. In one of the pole models, these amplitudes are significant and comparable with estimates based on the sigma model. However, calculation of off-mass-shell potential matrix elements reveals that they contribute less than 10% to circular polarization in 181Ta in two typical models of weak interactions employing neutral currents