Higgs-boson-mediated neutrinoless double-βdecay and neutrino mass in a Majoron model

We propose a simple extension of the standard model in which the neutrinoless double-{β} decay is a tree-level effect mediated by Higgs bosons and the neutrino mass begins to appear in the two-loop diagrams. The model also contains a massless Majoron, i.e., the Goldstone boson of the global symmetry of the lepton number, which is spontaneously broken at a scale close to that of the electroweak interaction. No unnaturally huge or tiny new scales are evoked. The Majoron coupling to the fermions is also two-loop suppressed.