Neutrinoless Double-$\beta$ Decay with Nonstandard Majoron Emission

Understand

We present a novel mode of neutrinoless double beta decay with emission of a light Majoron-like scalar particle phi.

• We assume it couples via an effective seven-dimensional operator with a (V+A) lepton current and (V+-A) quark currents leading to a long-range contribution that is unsuppressed by the light neutrino mass.
• We calculate the total double beta decay rate and determine the fully differential shape for this mode.
• We find that future double beta decay searches are sensitive to scales of the order Lambda_NP ~ 1 TeV for the effective operator and a light scalar m_phi < 0.2 MeV, based on ordinary double beta decay Majoron searches.