In this paper we discuss a minor modification of a previous SU(5) x A5 flavour model which exhibits at leading order golden ratio mixing and sum rules for the heavy and the light neutrino masses. Although this model could predict all mixing angles we
ll it fails in generating a sufficient large baryon asymmetry via the leptogenesis mechanism. We repair this deficit here, discuss model building aspects and give analytical estimates for the generated baryon asymmetry before we perform a numerical parameter scan. Our setup has only a few parameters in the lepton sector. This leads to specific constraints and correlations between the neutrino observables. For instance, we find that in the model considered only the neutrino mass spectrum with normal mass ordering and values of the lightest neutrino mass in the interval 10-18 meV are compatible with the current data on the neutrino oscillation parameters. With the introduction of only one NLO operator, the model can accommodate successfully simultaneously even at 1$sigma$ level the current data on neutrino masses, on neutrino mixing and the observed value of the baryon asymmetry.
After the successful determination of the reactor neutrino mixing angle theta_13 ~ 0.16 eq 0, a new feature suggested by the current neutrino oscillation data is a sizeable deviation of the atmospheric neutrino mixing angle theta_23 from pi/4. Using
the fact that the neutrino mixing matrix U = U_e^dagger U_ u, where U_e and U_ u result from the diagonalisation of the charged lepton and neutrino mass matrices, and assuming that U_ u has a i) bimaximal (BM), ii) tri-bimaximal (TBM) form, or else iii) corresponds to the conservation of the lepton charge L = L_e - L_mu - L_tau (LC), we investigate quantitatively what are the minimal forms of U_e, in terms of angles and phases it contains, that can provide the requisite corrections to U_ u so that theta_13, theta_23 and the solar neutrino mixing angle theta_12 have values compatible with the current data. Two possible orderings of the 12 and the 23 rotations in U_e, standard and inverse, are considered. The results we obtain depend strongly on the type of ordering. In the case of standard ordering, in particular, the Dirac CP violation phase delta, present in U, is predicted to have a value in a narrow interval around i) delta ~ pi in the BM (or LC) case, ii) delta ~ 3pi/2 or pi/2 in the TBM case, the CP conserving values delta = 0, pi, 2pi being excluded in the TBM case at more than 4sigma. In the addendum we discuss the implications of the latest 2013 data.
The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle theta_13 in the lepton sector. In this paper we show how a large theta_13 can arise from the charged lepton sector alone in the context of a
n SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.
We consider the possibility of several different mechanisms contributing to the $betabeta$-decay amplitude in the general case of CP nonconservation: light Majorana neutrino exchange, heavy left-handed (LH) and heavy right-handed (RH) Majorana neutri
no exchanges, lepton charge non-conserving couplings in SUSY theories with R-parity breaking. If the $betabeta$-decay is induced by, e.g., two non-interfering mechanisms, one can determine $|eta_i|^2$ and $|eta_j|^2$, $eta_i$ and $eta_j$ being the two fundamental parameters characterising these mechanisms, from data on the half-lives of two nuclear isotopes. In the case when two interfering mechanisms are responsible for the $betabeta$-decay, $|eta_i|^2$ and $|eta_j|^2$ and the interference term can be uniquely determined, in principle, from data on the half-lives of three nuclei. Given the half-life of one isotope, the positivity conditions $|eta_i|^2geq 0$ and $|eta_j|^2geq 0$ lead to stringent constraints on the half-lives of the other $betabeta$-decaying isotopes. These conditions, as well as the conditions for constructive (destructive) interference are derived and their implications are analysed in two specific cases. The method considered by us can be generalised to the case of more than two $betabeta$-decay mechanisms. It allows to treat the cases of CP conserving and CP nonconserving couplings generating the $betabeta$-decay in a unique way.
