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Roy, S., Morisi, S., Singh, N. N., & Valle, J. W. F. (2015). The Cabibbo angle as a universal seed for quark and lepton mixings. Phys. Lett. B, 748, 1–4.
Abstract: A model-independent ansatz to describe lepton and quark mixing in a unified way is suggested based upon the Cabibbo angle. In our framework neutrinos mix in a “Bi-Large” fashion, while the charged leptons mix as the “down-type” quarks do. In addition to the standard Wolfenstein parameters (lambda, A) two other free parameters (psi, delta) are needed to specify the physical lepton mixing matrix. Through this simple assumption one makes specific predictions for the atmospheric angle as well as leptonic CP violation in good agreement with current observations.
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Morisi, S., & Valle, J. W. F. (2013). Neutrino masses and mixing: a flavour symmetry roadmap. Fortschritte Phys.-Prog. Phys., 61(4-5), 466–492.
Abstract: Over the last ten years tri-bimaximal mixing has played an important role in modeling the flavour problem. We give a short review of the status of flavour symmetry models of neutrino mixing. We concentrate on non-Abelian discrete symmetries, which provide a simple way to account for the TBM pattern. We discuss phenomenological implications such as neutrinoless double beta decay, lepton flavour violation as well as theoretical aspects such as the possibility to explain quarks and leptons within a common framework, such as grand unified models.
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Morisi, S., Peinado, E., Shimizu, Y., & Valle, J. W. F. (2011). Relating quarks and leptons without grand unification. Physical Review D, 84(3), 036003.
Abstract: In combination with supersymmetry, flavor symmetry may relate quarks with leptons, even in the absence of a grand-unification group. We propose an SU(3) x SU(2) x U(1) model where both supersymmetry and the assumed A(4) flavor symmetries are softly broken, reproducing well the observed fermion mass hierarchies and predicting: (i) a relation between down-type quarks and charged lepton masses, and (ii) a correlation between the Cabibbo angle in the quark sector and the reactor angle theta(13) characterizing CP violation in neutrino oscillations.
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Morisi, S., & Peinado, E. (2010). S-4 model for quarks and leptons with maximal atmospheric angle. Phys. Rev. D, 81(8), 085015–8pp.
Abstract: We consider a model for quark and lepton masses and mixings based on S-4 flavor symmetry. The model contains six Higgs doublets where three of them give mass to the leptons, and the other three gives mass to the quarks. Charged fermion and quark masses arise from renormalizable interactions while neutrino Majorana masses are generated through effective dimension five Weinberg operator. From the study of the minimization of the scalar potential we found a residual μ<-> tau symmetry in the neutrino sector predicting zero reactor angle and maximal atmospheric angle and for the quark sector we found a four-zero texture. We give a fit of the mass hierarchies and mixing angles in the quark sector.
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Morisi, S., & Peinado, E. (2011). Admixture of quasi-Dirac and Majorana neutrinos with tri-bimaximal mixing. Phys. Lett. B, 701(4), 451–457.
Abstract: We propose a realization of the so-called bimodal/schizophrenic model proposed recently. We assume 54, the permutation group of four objects as flavor symmetry giving tri-bimaximal lepton mixing at leading order. In these models the second massive neutrino state is assumed quasi-Dirac and the remaining neutrinos are Majorana states. In the case of inverse mass hierarchy, the lower bound on the neutrinoless double beta decay parameter m(ee) is about two times that of the usual lower bound, within the range of sensitivity of the next generation of experiments.
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Morisi, S., Patel, K. M., & Peinado, E. (2011). Model for T2K indication with maximal theta(23) and trimaximal theta(12). Phys. Rev. D, 84(5), 053002–6pp.
Abstract: Recently T2K experiment gives hint in favor of large reactor angle theta(13). Most of the models, with tribimaximal mixing at the leading order, can not reproduce such a large mixing angle since they predict typically corrections for the reactor angle of the order theta(13) similar to lambda(2)(C), where lambda(C) similar to 0.2. In this paper, we discuss the possibility to achieve large theta(13) within the T2K region with maximal atmosphericmixing angle, sin(2)theta(23) = 1/2, and trimaximal solar mixing angle, sin(2)theta(12) = 1/3, through the deviation from the exact tribimaximal mixing. We derive the structure of neutrino mass matrix that leads to the large theta(13) leaving maximal theta(23) and trimaximal theta(12). It is shown that such a structure of neutrino mass matrix can arise in a model with S(4) flavor symmetry.
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Morisi, S., Nebot, M., Patel, K. M., Peinado, E., & Valle, J. W. F. (2013). Quark-lepton mass relation and CKM mixing in an A(4) extension of the minimal supersymmetric standard model. Phys. Rev. D, 88(3), 036001–8pp.
Abstract: An interesting mass relation between down-type quarks and charged leptons has been recently predicted within a supersymmetric SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) model based on the A(4) flavor symmetry. Here we propose a simple extension which provides an adequate full description of the quark sector. By adding a pair of vectorlike up quarks, we show how the CKM entries V-ub, V-cb, V-td and V-ts arise from deviations of the unitarity. We perform an analysis including the most relevant observables in the quark sector, such as oscillations and rare decays of kaons, B-d and B-s mesons. In the lepton sector, the model predicts an inverted hierarchy for the neutrino masses, leading to a potentially observable rate of neutrinoless double beta decay.
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Meloni, D., Morisi, S., & Peinado, E. (2011). Fritzsch neutrino mass matrix from S-3 symmetry. J. Phys. G, 38(1), 015003–10pp.
Abstract: We present an extension of the standard model (SM) based on the discrete flavor symmetry S-3 which gives a neutrino mass matrix with two-zero texture of Fritzsch type and nearly diagonal charged lepton mass matrix. The model is compatible with the normal hierarchy only and predicts sin(2) theta(13) approximate to 0.01 at the best-fit values of solar and atmospheric parameters and maximal leptonic CP violation.
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Meloni, D., Morisi, S., & Peinado, E. (2011). Neutrino phenomenology and stable dark matter with A(4). Phys. Lett. B, 697(4), 339–342.
Abstract: We present a model based on the A(4) non-Abelian discrete symmetry leading to a predictive five-parameter neutrino mass matrix and providing a stable dark matter candidate. We found an interesting correlation among the atmospheric and the reactor angles which predicts theta(23) similar to pi/4for very small reactor angle and deviation from maximal atmospheric mixing for large theta(13). Only normal neutrino mass spectrum is possible and the effective mass entering the neutrinoless double beta decay rate is constrained to be vertical bar m(ee)vertical bar > 4 x 10(-4) eV.
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Meloni, D., Morisi, S., & Peinado, E. (2011). Stability of dark matter from the D(4) x Z(2)(f) flavor group. Phys. Lett. B, 703(3), 281–287.
Abstract: We study a model based on the dihedral group D(4) in which the dark matter is stabilized by the interplay between a remnant Z(2) symmetry, of the same spontaneously broken non-abelian group, and an auxiliary Z(2)(f) introduced to eliminate unwanted couplings in the scalar potential. In the lepton sector the model is compatible with normal hierarchy only and predicts a vanishing reactor mixing angle, theta(13) = 0. Since m(nu 1) = 0, we also have a simple prediction for the effective mass in terms of the solar angle: vertical bar m(beta beta)vertical bar = vertical bar m(nu 2)vertical bar sin(2)theta circle dot similar to 10(-3) eV. There also exists a large portion of the model parameter space where the upper bounds on lepton flavor violating processes are not violated. We incorporate quarks in the same scheme finding that a description of the CKM mixing matrix is possible and that semileptonic K and D decays mediated by flavor changing neutral currents are under control.
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