Alternatives to the seesaw mechanism are explored in supersymmetric models with three right-handed or sterile neutrinos. Tree-level Yukawa couplings can be drastically suppressed in a natural way to give sub-eV Dirac neutrino masses. If, in addition, a (Formula presented) gauge symmetry broken at a large scale (Formula presented) is introduced, a wider range of possibilities opens up. The value of the right-handed neutrino mass (Formula presented) can be easily disentangled from that of (Formula presented) Dirac and Majorana neutrino masses at the eV scale can be generated radiatively through the exchange of sneutrinos and neutralinos. Dirac masses (Formula presented) owe their smallness to the pattern of light-heavy scales in the neutralino mass matrix. The smallness of the Majorana masses (Formula presented) is linked to a similar seesaw pattern in the sneutrino mass matrix. Two distinct scenarios emerge. In the first, with very small or vanishing (Formula presented) the physical neutrino eigenstates are, for each generation, either two light Majorana states with a mixing angle ranging from very small to maximal, depending on the ratio (Formula presented) or one light Dirac state. In the second scenario, with a large value of (Formula presented) the physical eigenstates are two nearly unmixed Majorana states with masses (Formula presented) and (Formula presented) In both cases, the (Formula presented)-breaking scale (Formula presented) is, in general, much smaller than that in the traditional seesaw mechanism.
|Number of pages||1|
|Journal||Physical Review D - Particles, Fields, Gravitation and Cosmology|
|Publication status||Published - 2001 Jan 1|
ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)