RESUMO
We present a novel mode of neutrinoless double-ß decay with emission of a light Majoron-like scalar particle Ï. 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-ß decay rate and determine the fully differential shape for this mode. We find that future double-ß decay searches are sensitive to scales of the order Λ_{NP}≈1 TeV for the effective operator and a light scalar m_{Ï}<0.2 MeV, based on ordinary double-ß decay Majoron searches. The angular and energy distributions can deviate considerably from that of two-neutrino double-ß decay, which is the main background. We point out possible ultraviolet completions where such an effective operator can emerge.
