  Models with spontaneously broken global lepton number can lead to a
pseudo-Goldstone boson as a long-lived dark matter candidate. Here we revisit
the case of singlet majoron dark matter and discuss multiple constraints. For
masses above MeV, this model could lead to a detectable flux of monochromatic
mass-eigenstate neutrinos, which have flavor ratios that depend strongly on the
neutrino mass hierarchy. We provide a convenient parametrization for the
loop-induced majoron couplings to charged fermions that allows us to discuss
three-generation effects such as lepton flavor violation. These couplings are
independent of the low-energy neutrino parameters but can be constrained by the
majoron decays into charged fermions.
