Small and calculable Dirac neutrino mass

The Grimus–Neufeld Model with FlexibleSUSY at One-Loop

The Grimus–Neufeld model can explain the smallness of measured neutrino masses by extending the Standard Model with a single heavy neutrino and a second Higgs doublet, using the seesaw mechanism and radiative mass generation. The Grimus–Lavoura approximation allows us to calculate the light neutrino masses analytically. By inverting these analytic expressions, we determine the neutrino Yukawa couplings from the measured neutrino mass differences and the neutrino mixing matrix. Short-cutting the full renormalization of the model, we implement the Grimus–Neufeld model in the spectrum calculator FlexibleSUSY and check the consistency of the implementation. These checks hint that FlexibleSUSY is able to do the job of numerical renormalization in a restricted parameter space. As a summary, we also comment on further steps of the implementation and the use of FlexibleSUSY for the model.

Neutrinoless Double-β Decay with Nonstandard Majoron Emission

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

Relations between neutrino and charged fermion masses

We find an intriguing relation between neutrino and charged fermion masses, |m(ν₃)² -m(ν₁)²|:(m(ν₂)²-m(ν₁)²)::V(tb)⁴m(τ)²m(b)²/m(t)²:V(cs)⁴m(μ)²m(s)²/m(c)². We further indicate this relation can be predicted by a left-right symmetric model.