DecayL0→νlγin gauge theories of weak and electromagnetic interactions

Results are presented of a calculation of the rate for the decay $L^0\to {\nu }_l\gamma$, where $L^0=E^0$, $M^0$ is a neutral heavy lepton occurring in certain gauge theories of weak and electromagnetic interactions. This rate is compared with that for the semileptonic decay mode $L^0\to l^{-}{\pi }^{+}$, and it is found that, although the former is of order ${\alpha }^3$, whereas the latter is of order ${\alpha }^2$, the $L^0\to {\nu }_l\gamma$ rate can actually exceed the $L^0\to l^{-}{\pi }^{+}$ rate in models which also have a charged heavy lepton $L^{+}$.