The Seesaw with Many Right-Handed Neutrinos

Understand

There are no upper limits on the possible number of massive, singlet (right--handed) neutrinos that may participate in the seesaw mechanism, and some string constructions motivate seesaw models with up to O(100) right--handed neutrinos.

• In this case, the seesaw mass scale can be significantly higher than that in the traditional scheme with just 3 right--handed neutrinos.
• We consider the possible phenomenological implications of such models, in particular, for lepton-flavour violation and electric dipole moments.
• Since the neutrino masses depend on the Majorana mass scale linearly, while supersymmetric loop corrections depend on it logarithmically, the magnitude of lepton-flavour- and CP-violating transitions may increase with the multiplicity of the right--handed neutrinos and may be enhanced by orders of magnitude.