A hidden hierarchy of neutrino masses

Abstract

The Dirac masses of neutrinos can exhibit a strong hierarchy even if the Majorana masses of the right-handed neutrinos are degenerate and the hierarchy of the mass scales governing the oscillations of solar and atmospheric neutrinos is rather small. This phenomenon results from the see-saw mechanism and the algebraic structure of the effective mass operator for the active neutrinos. The large hierarchy of the Dirac masses is drastically modified by a symmetric unitary matrix R acting in the flavor space. A realistic pattern of neutrino masses and mixing is obtained. Maximal mixing for atmospheric neutrinos is attributed to the charged lepton sector. Large mixing in solar neutrino oscillations is due to the neutrino sector. Small U e3 is a natural consequence of the model. The masses of the active neutrinos are given by µ 3 ≈ ∆m 2 @ and µ 1 /µ 2 ≈ tan 2 θ ⊙ .

Degenerate minimal see-saw and leptogenesis

“…To the extent to which the effects of the this right-chiral neutrino can be neglected in the see-saw formula the results considered here apply also to the three neutrino models. There are also models in which the exchange of one of the right-chiral neutrinos gives mass solely to the heaviest light neutrino and the minimal see-saw formalism can be applied to the ν 1 , ν 2 sector [22].…”

Low scale gravity as the source of neutrino masses?

“…The theoretical counterpart of this situation is that it is possible to postulate several textures of mass matrices which are consistent with present data. There are a large number of studies where this approach has been developed, for example see [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35].…”