Validity of quasi-degenerate neutrino mass models and their predictions on baryogenesis Original Research Article

Quasi-degenerate neutrino mass models (QDN) which can explain the current data on neutrino masses and mixings, are studied. In the first part, we study the effect of CP-phases on QDN mass matrix (image) obeying μ–τ symmetry in normal hierarchical (QD-NH) and inverted hierarchical (QD-IH) patterns. The numerical predictions are consistent with observed data on (i) solar mixing angle image which lies below tri-bimaximal (TBM) value, (ii) absolute neutrino masses consistent with image decay mass parameter image and (iii) cosmological upper bound image. image is parameterized using only two unknown parameters image within μ–τ symmetry. The second part deals with the estimation of observed baryon asymmetry of the universe (BAU) where we consider the Majorana CP violating phases image and the Dirac neutrino mass matrix image. image is taken as either the charged lepton or the up quark mass matrix. α, β is derived from the heavy right-handed Majorana mass matrix image. image is generated from image and image through inversion of Type-I seesaw formula. The predictions for BAU are nearly consistent with observations for flavoured thermal leptogenesis scenario for Type-IA in both QD-NH and QD-IH models. We also observe some enhancement effects in flavour leptogenesis compared to non-flavour leptogenesis by a magnitude of order one. In non-thermal leptogenesis QD-NH Type-IA is the only model consistent with observed data on baryon asymmetry. QD-NH model appears to be more favourable than those of QD-IH. The predicted inflaton mass needed to produce the BAU is found to be image corresponding to the reheating temperature image. The present analysis shows that the three absolute neutrino masses may exhibit quasi-degenerate pattern in nature.