Quasi-Degenerate Neutrino Masses with Normal and Inverted Hierarchy

The effects of CP-phases on the three absolute quasi-degenerate Majorana neutrino (QDN) masses are stud-ied with neutrino mass matrices obeying {mu} - {tau} symmetry for normal as well as inverted hierarchical mass patterns. We have made further investigations on 1) the prediction of solar mixing angle which lies below tri-bimaximal mixing value in consistent with neutrino oscillation observational data, 2) the prediction on absolute neutrino mass parameter (mee) in 0{ u}{beta}{beta} decay, and 3) cosmological bound on the sum of the three absolute neutrino masses. The numerical analysis is carried out through the parameterization of neu- trino mass matrices using only two unknown parameters ({epsilon}, {eta}) within {mu} - {tau} symmetry. The results show the validity of QDN mass models in both normal and inverted hierarchical patterns. These models are far from discrimination and hence not yet ruled out. The results presented in this article are new and have subtle ef- fects in the discrimination of neutrino mass models.

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

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 obeying $mu-tau$ symmetry in normal hierarchical (QD-NH) and inverted hierarchical (QD-IH) patterns.The numerical predictions are consistent with observed data on solar mixing angle, absolute neutrino mass parameter consistent with neutrinoless double beta decay mass parameter and sum of three absolute neutrino masses from cosmological bound.The neutrino mass matrix is parameterized using only two unknown parameters. The second part deals with the estimation of observed baryon asymmetry of the universe. The prediction is nearly consistent with observation with flavoured thermal leptogenesis scenario. QD-NH model appears to be more favourable than those of QD-IH models.The present analysis shows that the three absolute neutrino masses may exhibit quasi-degenerate pattern in nature. They are far from discrimination at the moment.

Flavour leptogenesis with tribimaximal mixings and beyond

We compute and compare the baryon asymmetry of the universe in thermal leptogenesis scenario with and without flavour effects for different neutrino mass models namely degenerate, inverted hierarchical and normal hierarchical models, with tribimaximal mixings and beyond. Considering three possible diagonal forms of Dirac neutrino mass matrices $m_{LR}$, the right-handed Majorana mass matrices $M_{RR}$ are constructed from the light neutrino mass matrices $m_{LL}$ through the inverse seesaw formula. The normal hierarchical model is found to give the best predictions of the baryon asymmetry for both cases. This analysis serves as an additional information in the discrimination of the presently available neutrino mass models. Moreover, the flavour effects is found to give enhancement of the baryon asymmetry in thermal leptogenesis.

Degenerate neutrino mass models revisited

A parametrisation of the degenerate neutrino mass matrix obeying $mu -tau$ symmetry, is introduced for detailed numerical analysis. As a continuation of our earlier work on normal and inverted hierarchical models, the present parametrisation for degenerate models has the ability to lower the solar mixing angle below the tri-bimaximal value $tan^{2}theta_{12}=0.5$, while maintaining the condition of maximal atmospheric mixing angle and zero reactor angle. The combined data on the mass-squared differences derived from various oscillation experiments, and also from the bounds on absolute neutrino masses in $0 ubetabeta$ decay and cosmology, gives certain constraints on the validity of the degenerate models.