We show that a modification of the Cabibbo theory leads to identical results concerning the leptonic decays of hyperons but additionally contains the $\Delta I=\frac{1}{2}$ rule. The $\Delta I=\frac{1}{2}$ rule so obtained is weakly broken, but the deviations are not inconsistent with experiment. (The estimated rate for $K^{+}\to {\pi }^{+}{\pi }^0$ is somewhat less than experimentally observed.) The model differs from Cabibbo's theory in that $G_V \frac{\left(\beta \mathrm{decay}\right)}{GV\left(\mathrm{muon}\mathrm{decay}\right)}=1\mathrm{}$ rather than $cos\theta =0.966\mathrm{}$. Branching ratios of the intermediate bosons are estimated.

• Received 9 February 1966

DOI:https://doi.org/10.1103/PhysRev.156.1698