New class of Majoron-emitting double-β decays

Motivated by the excess events that have recently been found near the end points of the double-β decay spectra of several elements, we reexamine models in which double-β decay can proceed through the neutrinoless emission of massless Nambu-Goldstone bosons (Majorons). Noting that models proposed to date for this process must fine-tune either a scalar mass or a VEV to be less than 10 keV, we introduce a new kind of Majoron which avoids this …