Pionic Decays of Hyperons and Universal Weak Coupling

The pionic decays of hyperons are analyzed in terms of the pole approximation of Feldman, Matthews, and Salam and the preceding paper. It is found that all the available experimental data are consistent with the universal weak coupling scheme, provided all the strong coupling constants have the same magnitude as the usual pion-nucleon coupling constant. In this universal weak coupling scheme, all the (dimensionless) weak coupling constants which appear in the residues of the pole terms have the same magnitude as the weak coupling constant determined in the preceding paper for the leptonic decays of pions and kaons. It is argued that this scheme is a dispersion theoretic version of the usual $V-A$ theory of the weak interaction. The above universal coupling scheme predicts unambiguously that the $S$ wave dominates in ${\Sigma }^{+}\to n+{\pi }^{+}$ and the $P$ wave dominates in ${\Sigma }^{-}\to n+{\pi }^{-}$, and also establishes some of the relative signs of the strong coupling constants. It is shown that there appears no other universal scheme of both the strong and weak coupling constants. In particular, the above universal weak coupling scheme is not compatible with the usual unitary symmetry relations for the strong coupling constants, through this conclusion depends very sensitively on the mixing parameter in the unitary symmetry relations. The main consequences and a discussion of the above universal coupling scheme are given in the last section.