Abstract
The notion of U(1) lepton number (which may only be softly broken) is applied to models of dark matter which interacts with leptons. Previous scotogenic models of Majorana or Dirac neutrino mass are shown to be derivable in this framework without additional symmetries. Only complete renormalizable theories are considered. A new explicit class of models with Zn (n≥5) lepton and dark symmetry for Dirac neutrinos is derived, as well as a new example of Z3 dark symmetry.
Highlights
Two outstanding fundamental issues in particle physics and astroparticle physics are neutrinos and dark matter. They have been shown [1] to be intimately connected in all simple models of dark matter, with dark parity πD derivable from lepton parity πL with the factor (−1)2j for a particle of spin j. To explore further this connection, it is assumed that lepton number may be imposed as a global U (1)L symmetry in dark-matter extensions of the standard model (SM) of quark and lepton interactions
The U (1)L is used to forbid a tree-level Majorana or Dirac neutrino mass, whereas its soft breaking will usher in a radiative Majorana or Dirac neutrino mass through dark matter, i.e. the scotogenic mechanism
The intrinsic connection between lepton number and dark symmetry has been demonstrated with three examples in the case of Majorana neutrinos where U (1)L is broken softly to Z2 lepton parity πL
Summary
Two outstanding fundamental issues in particle physics and astroparticle physics are neutrinos and dark matter. This second example shows the power of U (1)L in combination of the chosen particle content in acquiring radiative Majorana neutrino mass together with a dark symmetry. Since ρ0 has no coupling to Z, it is a viable dark-matter candidate in this case and the dark symmetry U (1)D emerges as a consequence of softly broken U (1)L together with the chosen particle content.
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