Majorons and muon decay

The existence of a massless Goldstone boson coupling to neutrinos in theories with spontaneous violation of a global $B-L$ symmetry may be consequential in precision measurements of the parameters in muon decay. We calculate the decay parameters for $\mu \to \mathrm{eMM}$, where the Majoron $M$ is the Goldstone boson, and discuss limits on the Majoron-neutrino coupling.