Neutrino masses, mixing and leptogenesis in a two Higgs doublet model "for the third generation"

We examine neutrino oscillations in a two Higgs doublet model (2HDM) in which the second doublet couples only to the third generation right-handed up-fermions, i.e., to t(R) and to N-3 which is the heaviest right-handed Majorana neutrino. The inherently large tan P of this model can naturally account for the large top mass and, based on a quark-lepton similarity ansatz, when embedded into a see-saw mechanism it can also account for the observed neutrino masses and mixing angles giving a very small theta(13): -0.017 less than or similar to theta(13) less than or similar to 0.021 at 99% CL, and a very restrictive prediction for the atmospheric mixing angle: 42.9 degrees less than or similar to theta(atm) less than or similar to 45.2 degrees at 99% CL. The large value of tan beta also sets the mass scale of the heaviest right-handed Majorana neutrino N-3 and triggers successful leptogenesis through a CP-asymmetry in the decays of the N-1 (lightest right-handed Majorana) which is tan(2)beta enhanced compared to the CP-asymmetry obtained in models for leptogenesis with one Higgs doublet or in the MSSM. This enhancement allows us to relax the lower bound on M-N1 and consequently also the lower bound on the reheating temperature of the early universe. (c) 2006 Elsevier B.V. All rights reserved.