Enhancement of the parity-violating isospin-changing one-pion-exchange potential for three-triplet gauge models has been found with respect to the standard weak-Hamiltonian model. In the case of the Bég-Zee model, which allows for the neutral hadron-current coupling to neutrinos, there is an enhancement by at least a factor of 10. The Lee-Prentki-Zumino and the Georgi-Glashow models are also discussed. The role of Fierz transformations has been investigated in detail. It has been suggested that the detection of an angular $\gamma$ asymmetry comparable with circular $\gamma$ polarization in thermal-neutron capture, as well as larger resonance than expected in the decay process of lithium, can be meaningful substantiation of unified theories of weak and electromagnetic interactions.

• Received 26 September 1974

DOI:https://doi.org/10.1103/PhysRevD.11.1331