Lepton flavour violation in a left-right symmetric model

Abstract

We consider in this paper a Left-Right symmetric gauge model in which a global lepton-number-like symmetry is introduced and broken spontaneously at a scale ω that could be as low as 10⁴ GeV or so. The corresponding physical Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level flavour-violating couplings to the charged fermions, leading to sizeable majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a leptonic variant of the model and show that the branching ratios for μ→e+J, τ→e+J and τ→μ+J decays can be large enough to fall within the sensitivities of future μ and τ factories. On the other hand the left-right gauge symmetry breaking scale may be as low as few TeV.