Normal versus inverted hierarchical models within $\mu-\tau$ symmetry

Abstract

We make a theoretical attempt to compare the predictions from normal and inverted hierarchical models, within the framework of $\mu-\tau$ symmetry. We consider three major theoretical issues in a self consistent ways, viz., predictions on neutrino mass and mixing parameters, stability under RG analysis in MSSM, and baryogenesis through leptogenesis. We further extend our earlier works on parametrisation of neutrino mass matrices using only two parameters, in addition to an overall mass scale $m_0$, and the ratio of these two parameters fixes the value of solar mixing angle. Such parametrisation though phenomenological gives a firm handle on the analysis of the mass matrices and predicts lower values of solar mixing angle in the range $\tan^2\theta_{12}=0.50-0.35$.We check the stability of the model under radiative corrections in MSSM for large $\tan\beta\sim 58-60$ region and observe that the evolution of $\bigtriangleup m^2_{21}$ with energy scale, is highly dependent on the input high scale value of solar mixing angle. Solar angle predicted by tri-bimaximal mixings and also values lower than this, do not lead to stability of the model. Similarly, the evolution of the atmospheric mixing angle with energy scale at large $\tan\beta$ values, shows sharp decrease for the case with non-zero value of m_3. We apply these mass matrices to estimate the baryon asymmetry of the universe in a self consistent way and find that normal hierarchical model leads to the best result. Considering all these three pieces of theoretical investigations, we may conclude that normal hierarchical model is more favourable in nature.