On the nature of the fourth generation neutrino and its implications

Abstract

We consider the neutrino sector of a Standard Model with four generations. While the three light neutrinos can obtain their masses from a variety of mechanisms with or without new neutral fermions, fourth-generation neutrinos need at least one new relatively light right-handed neutrino. If lepton number is not conserved this neutrino must have a Majorana mass term whose size depends on the underlying mechanism for lepton number violation. Majorana masses for the fourth generation neutrinos induce relative large two-loop contributions to the light neutrino masses which could be even larger than the cosmological bounds. This sets strong limits on the mass parameters and mixings of the fourth generation neutrinos.

To be published. Few typos corrected, references updated

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Cited by in corpus (6)

• Right-handed Neutrinos and $R(D^{(\ast )})$
• Higgs data confronts Sequential Fourth Generation Fermions in the Higgs Triplet Model
• Higgs data does not rule out a sequential fourth generation with an extended scalar sector
• Two-loop renormalization group equations for right-handed neutrino masses and phenomenological implications
• Gauged $L_e-L_{\mu }-L_{\tau }$ symmetry, fourth generation, neutrino mass and dark matter
• Neutrino parameters in the Planck-scale lepton number breaking scenario with extended scalar sectors