Radiative Inverse Seesaw: Verifiable New Mechanism of Neutrino Mass

If the canonical seesaw mechanism alone is responsible for neutrino mass, i.e. mν ≃ −m 2 D/mN , it can neither be proved nor disproved at the TeV energy scale. A new verifiable mechanism of neutrino mass is proposed, using the inverse seesaw, with new physics at the TeV scale, such that mν ≃ m 2 DǫL/m 2 N , where ǫL is a two-loop effect. Dark-matter candidates also appear naturally. Introduction : Neutrinos have mass, but the mechanism for it to occur remains a topic of theoretical study. The reason is that, unlike other charged fermions such as the electron or the quarks, the neutrinos are electrically neutral, and could have either Dirac or Majorana masses or both. The prevalent thinking is that in addition to the left-handed neutrino νL in the electroweak lepton doublet (ν, l)L of the standard SU(3)C × SU(2)L × U(1)Y gauge model of particle interactions, there is also a right-handed neutrino NR (for each of the three families of quarks and leptons), which is a singlet. Thus it has no gauge interactions, and couples only to the Higgs doublet Φ = (φ, φ), i.e. fN̄R(νLφ 0 − lLφ ), so that a Dirac mass is obtained as φ acquires a vacuum expectation value v = 〈φ〉, linking νL with NR. If this is the only allowed additional term, then NR is simply νR, i.e. ν is a four-component Dirac spinor with mass mD = fv, and additive lepton number L is conserved. However, since NR is a singlet, it should be allowed a Majorana mass mN . Hence the 2 × 2 mass matrix spanning ν̄L and NR is given by MνN = (