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Register a new userPartial $mu-tau$ Textures and Leptogenesis
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Motivated by the recent results from Daya Bay, Reno and Double Chooz Collaborations, we study the consequences of small departures from exact $mu-tau$ symmetry in the neutrino sector, to accommodate a non-vanishing value of the element $V_{e3}$ from the leptonic mixing matrix. Within the see-saw framework, we identify simple patterns of Dirac mass matrices that lead to approximate $mu-tau$ symmetric neutrino mass matrices, which are consistent with the neutrino oscillation data and lead to non-vanishing mixing angle $V_{e3}$ as well as precise predictions for the CP violating phases. We also show that there is a transparent link between neutrino mixing angles and see-saw parameters, which we further explore within the context of leptogenesis as well as double beta decay phenomenology.
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We discuss the viability of the $mu$--$tau$ interchange symmetry imposed on the neutrino mass matrix in the flavor space. Whereas the exact symmetry is shown to lead to textures of completely degenerate spectrum which is incompatible with the neutrino oscillation data, introducing small perturbations into the preceding textures, inserted in a minimal way, lead however to four deformed textures representing an approximate $mu$--$tau$ symmetry. We motivate the form of these `minimal textures, which disentangle the effects of the perturbations, and present some concrete realizations assuming exact $mu$--$tau$ at the Lagrangian level but at the expense of adding new symmetries and matter fields. We find that all these deformed textures are capable to accommodate the experimental data, and in all types of neutrino mass hierarchies, in particular the non-vanishing value for the smallest mixing angle.
We study the consequences of the $Z_2$-symmetry behind the $mu$--$tau$ universality in neutrino mass matrix. We then implement this symmetry in the type-I seesaw mechanism and show how it can accommodate all sorts of lepton mass hierarchies and generate enough lepton asymmetry to interpret the observed baryon asymmetry in the universe. We also show how a specific form of a high-scale perturbation is kept when translated via the seesaw into the low scale domain, where it can accommodate the neutrino mixing data. We finally present a realization of the high scale perturbed texture through addition of matter and extra exact symmetries.
We study a $mu - tau$ reflection symmetry in neutrino sector realized at the GUT scale in the context of the seesaw model. In our scenario, the exact $mu - tau$ reflection symmetry realized in the basis where the charged lepton and heavy Majorana mass matrices are diagonal, leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetry extension of the seesaw model with appropriate values of $tanbeta$, the renormalization group (RG) evolution from the GUT scale to seesaw scale can induce a successful leptogenesis. It is shown that the right amount of the baryon asymmetries $eta_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale in our scenario, so that the well-known gravitino problem is safely avoided. In this work, we consider both flavor dependent and flavor independent leptogenesis, and demonstrate how they lead to different amounts of baryon asymmetries in detail.
We consider an exact mu-tau reflection symmetry in neutrino sectorrealized at the GUT scale in the context of the seesaw model with and without supersymmetry. Assuming the two lighter heavy Majorana neutrinos are degenerate at the GUT scale, it is shown that the renormalization group (RG) evolution from the GUT scale to the seesaw scale gives rise to breaking of the mu-tau symmetry and a tiny splitting between two degenerate heavy Majorana neutrino masses as well as small variations of the CP phases in Y_nu, which are essential to achieve a successful leptogenesis. Such small RG effects lead to tiny deviations of theta_{23} from the maximal value and the CP phase delta_{CP} from pi/2 imposed at the GUT scale due to mu-tau reflection symmetry. In our scenario, the required amount of the baryon asymmetry eta_B can be generated via so-called resonant e-leptogenesis, in which the wash-out factor concerned with electron flavor plays a crucial role in reproducing a successful leptogenesis. We show that CP violation responsible for the generation of baryon asymmetry of our universe can be directly linked with CP violation measurable through neutrino oscillation as well as neutrino mixing angles theta_{12} and theta_{13}. We expect that, in addition to the reactor and long baseline neutrino experiments, the measurements for the supersymmetric parameter tan{beta} at future collider experiments would serve as an indirect test of our scenario of baryogenesis based on the mu-tau reflection symmetry.
We propose a $mu-tau$ reflection symmetric Littlest Seesaw ($mutau$-LSS) model. In this model the two mass parameters of the LSS model are fixed to be in a special ratio by symmetry, so that the resulting neutrino mass matrix in the flavour basis (after the seesaw mechanism has been applied) satisfies $mu-tau$ reflection symmetry and has only one free adjustable parameter, namely an overall free mass scale. However the physical low energy predictions of the neutrino masses and lepton mixing angles and CP phases are subject to renormalisation group (RG) corrections, which introduces further parameters. Although the high energy model is rather complicated, involving $(S_4times U(1))^2$ and supersymmetry, with many flavons and driving fields, the low energy neutrino mass matrix has ultimate simplicity.
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