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

Abstract

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(beta) of this model can naturally account for the large top mass and, based on a quark-lepton similarity ansatz, when embedded into a seesaw mechanism it can also account for the observed neutrino masses and mixing angles giving a very small θ_{13}: -0.017 < θ_{13} < 0.021 at 99% CL, and a very restrictive prediction for the atmospheric mixing angle: 42.9^0 < θ_{atm} < 45.2^0 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_{N_1} and consequently also the lower bound on the reheating temperature of the early universe.

2 pages, 2 figures. Important changes made in v2: 1) improved presentation of leptogenesis and 2) a more elaborate discussion on the assumed texture zeros in the neutrino Yukawa sector. Important changes made in v3: minor changes added to emphasize that in our model the CP-asymmetry in the decays of the lightest Majorana is enhanced by tan^2(beta)~O(100) compared to models with one Higgs doublet as well as with respect to the MSSM