The invariance of strong interactions under $G$, the product of charge symmetry and charge conjugation, has important consequences for strangeness-conserving lepton interactions. According to the $G$-transformation properties of the strongly interacting "currents," we may divide the primary weak interactions into two classes. The first class includes the conventional nucleon-lepton Fermi interaction, and is the only class that contributes to the $\beta$-decay coupling constants. Unambiguous tests for the existence of second-class interactions include: (a) induced scalar term in ${\mu }^{-}$ absorption, (b) inequality of certain small correction terms in ${\mathrm{B}}^{12}$ and ${\mathrm{N}}^{12}$, or in ${\mathrm{Li}}^8$ and ${\mathrm{B}}^8$ $\beta$ decay, (c) inequality in rates of ${\Sigma }^{\pm }\to {\Lambda }^0+e^{\pm }+\nu$. Absence of second-class interactions would indicate a deep relation between isotopic spin and weak interactions; for example, the recent Feynman-Gell-Mann theory predicts that all vector weak interactions are first class. The presence of second-class interactions would mean that the usual Fermi interaction is insufficient, and must be supplemented by terms involving strange particles. Some general remarks are also made about the relations between ($l^{-}, \overline{\nu }$) and ($l^{+}, \nu$) processes, and we prove the following useful theorem: no interference between $V$ and $A$ may occur in any experiment which treats both leptons identically and in which no parity nonconservation effects are measured, providing that we may neglect the mass and charge of the leptons.

• Received 25 June 1958

DOI:https://doi.org/10.1103/PhysRev.112.1375