1,948 research outputs found

    Neutrino masses and mixing from flavour antisymmetry

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    We discuss consequences of assuming (ii) that the (Majorana) neutrino mass matrix MνM_\nu displays flavour antisymmetry, SνTMνSν=MνS_\nu^T M_\nu S_\nu=-M_\nu with respect to some discrete symmetry SνS_\nu contained in SU(3)SU(3) and (iiii) SνS_\nu together with a symmetry TlT_l of the Hermitian combination MlMlM_lM_l^\dagger of the charged lepton mass matrix forms a finite discrete subgroup GfG_f of SU(3)SU(3) whose breaking generates these symmetries. Assumption (ii) leads to at least one massless neutrino and allows only four textures for the neutrino mass matrix in a basis with a diagonal SνS_\nu if it is assumed that the other two neutrinos are massive. Two of these textures contain a degenerate pair of neutrinos.Assumption (iiii) can be used to determine the neutrino mixing patterns. We work out these patterns for two major group series Δ(3N2)\Delta(3 N^2) and Δ(6N2)\Delta(6 N^2) as GfG_f. It is found that all Δ(6N2)\Delta(6 N^2) and Δ(3N2)\Delta(3 N^2) groups with even NN contain some elements which can provide appropriate SνS_\nu. Mixing patterns can be determined analytically for these groups and it is found that only one of the four allowed neutrino mass textures is consistent with the observed values of the mixing angles θ13\theta_{13} and θ23\theta_{23}. This texture corresponds to one massless and a degenerate pair of neutrinos which can provide the solar pair in the presence of some perturbations. The well-known groups A4A_4 and S4S_4 provide examples of the groups in respective series allowing correct θ13\theta_{13} and θ23\theta_{23}. An explicit example based on A4A_4 and displaying a massless and two quasi degenerate neutrinos is discussed.Comment: 22 pages, 1 figur

    Universal 2-3 symmetry

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    Possible maximal mixing seen in the oscillations of the atmospheric neutrinos has led to postulate of a μ\mu-τ\tau symmetry which interchanges νμ\nu_\mu and ντ\nu_\tau. We argue that such symmetry need not be special to neutrinos but can be extended to all fermions. The assumption that all fermion mass matrices are approximately invariant under interchange of the second and the third generation fields is shown to be phenomenologically viable and has interesting consequences. In the quark sector, the smallness of VubV_{ub} and VcbV_{cb} can be a consequences of this approximate 2-3 symmetry. The same approximate symmetry can simultaneously lead to large atmospheric mixing angle and can describe the leptonic mixing quite well provided the neutrino spectrum is quasi degenerate. We present this scenario, elaborate on its consequences and discuss its realization.Comment: 13 pages, 1 figur

    Summary of Model Predictions for Ue3U_{e3}

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    We present a short discussion on the expected magnitude of Ue3|U_{e3}| in the context of various scenarios proposed to describe neutrino masses and mixing. Generic expectation is relatively large (>0.05>0.05) values for \ue3 which occur in many well-motivated theoretical scenarios and models.Comment: Updated version of the talk presented at the 5th Workshop on "Neutrino Oscillations and their Origin (NOON2004)", February 11-15, Tokyo, Japa

    Constraints on flavour-dependent long-range forces from atmospheric neutrino observations at Super-Kamiokande

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    In the minimal standard model it is possible to gauge any one of the following global symmetries in an anomaly free way: (i)LeLμL_{e}-L_{\mu}, (ii) LeLτL_{e}-L_{\tau} or (iii) LμLτL_{\mu}-L_{\tau}. If the gauge boson corresponding to (i) or (ii) is (nearly) massless then it will show up as a long range composition dependent fifth force between macroscopic objects. Such a force will also influence neutrino oscillations due to its flavour-dependence. We show that the latter effect is quite significant in spite of very strong constraints on the relevant gauge couplings from the fifth force experiments. In particular, the LeLμ,τL_{e}- L_{\mu,\tau} potential of the electrons in the Sun and the earth is shown to suppress the atmospheric neutrino νμντ\nu_\mu \to \nu_\tau oscillations which have been observed at Super-Kamiokande. The Super-K data of oscillation of multi-GeV atmospheric neutrinos can be used to put an upper bound on coupling αeτ<6.4×1052\alpha_{e\tau}< 6.4 \times 10^{-52} and αeμ<5.5×1052\alpha_{e\mu}< 5.5 \times 10^{-52}at 90% CL when the range of the force is the earth-sun distance. This is an improvement by two orders on the earlier fifth force bounds in this range.Comment: 5 pages Latex, 3 figure

    Pseudo-Dirac neutrinos from flavour dependent CP symmetry

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    Discrete residual symmetries and flavour dependent CP symmetries consistent with them have been used to constrain neutrino mixing angles and CP violating phases. We discuss here role of such CP symmetries in obtaining a pseudo-Dirac neutrino which can provide a pair of neutrinos responsible for the solar splitting. It is shown that if (a) 3×33\times 3 Majorana neutrino matrix MνM_\nu is invariant under a discrete Z2×Z2Z_2\times Z_2 symmetry generated by S1,2S_{1,2}, (b) CP symmetry XX transform MνM_\nu as XTMνX=MνX^T M_\nu X=M_\nu^*, and (c) XX and S1,2S_{1,2} obey consistency conditions XS1,2X=S2,1X S_{1,2}^* X^\dagger=S_{2,1}, then two of the neutrino masses are degenerate independent of specific forms of XX, S1S_1 and S2S_2. Explicit examples of this result are discussed in the context of Δ(6n2)\Delta(6 n^2) groups which can also be used to constrain neutrino mixing matrix UU. Degeneracy in two of the masses does not allow complete determination of UU but it can also be fixed once the perturbations are introduced. We consider explicit perturbations which break Z2×Z2Z_2\times Z_2 symmetries but respect CP. These are shown to remove the degeneracy and provide a predictive description of neutrino spectrum. In particular, a correlation sin2θ23sinδCP=±Im[p]\sin 2\theta_{23}\sin\delta_{CP}=\pm {\rm Im}[p] is obtained between the atmospheric mixing angle θ23\theta_{23} and the CP violating phase δCP\delta_{CP} in terms of a group theoretically determined phase factor pp. Experimentally interesting case θ23=π4\theta_{23}=\frac{\pi}{4}, δCP=±π2\delta_{CP}=\pm \frac{\pi}{2} emerges for groups which predict purely imaginary pp. We present detailed predictions of the allowed ranges of neutrino mixing angles, phases and the lightest neutrino mass for three of the lowest Δ(6n2)\Delta(6 n^2) groups with n=2,4,6n=2,4,6.Comment: 17 pages, 4 figures; Minor modification, published versio

    Generalized μ\mu-τ\tau symmetry and discrete subgroups of O(3)

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    The generalized μ\mu-τ\tau interchange symmetry in the leptonic mixing matrix UU corresponds to the relations: Uμi=Uτi|U_{\mu i}|=|U_{\tau i}| with i=1,2,3i=1,2,3. It predicts maximal atmospheric mixing and maximal Dirac CP violation given θ130\theta_{13} \neq 0. We show that the generalized μ\mu-τ\tau symmetry can arise if the charged lepton and neutrino mass matrices are invariant under specific residual symmetries contained in the finite discrete subgroups of O(3)O(3). The groups A4A_4, S4S_4 and A5A_5 are the only such groups which can entirely fix UU at the leading order. The neutrinos can be (a) non-degenerate or (b) partially degenerate depending on the choice of their residual symmetries. One obtains either vanishing or very large θ13\theta_{13} in case of (a) while only A5A_5 can provide θ13\theta_{13} close to its experimental value in the case (b). We provide an explicit model based on A5A_5 and discuss a class of perturbations which can generate fully realistic neutrino masses and mixing maintaining the generalized μ\mu-τ\tau symmetry in UU. Our approach provides generalization of some of the ideas proposed earlier in order to obtain the predictions, θ23=π/4\theta_{23}=\pi/4 and δCP=±π/2\delta_{\rm CP} = \pm \pi/2.Comment: 18 page

    Fermion number conservation and two Higgs doublet models without tree level flavour changing neutral currents

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    The charged fermion mass matrices are always invariant under U(1)3U(1)^3 symmetry linked to the fermion number transformation. A class of two Higgs doublet models (2HDM) can be identified by requiring that the definition of this symmetry in an arbitrary weak basis be independent of Higgs parameters such as the ratio of the Higgs vacuum expectation values. The tree level flavour changing neutral currents normally present in 2HDM are absent in this class of models but unlike the type I or type II Higgs doublet models, the charged Higgs couplings in these models contain additional flavour dependent CP violating phases. These phases can account for the recent hints of the beyond standard model CP violation in the BdB_d and BsB_s mixing. In particular, there is a range of parameters in which new phases do not contribute to the KK meson CP violation but give identical new physics contribution to the BdB_d and BsB_s meson mixing. Specific model realizations of the above scenario are briefly discussed.Comment: 12 page

    Predictive Framework with a Pair of Degenerate Neutrinos at a high scale

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    Radiative generation of the solar scale Δ\Delta_{\odot} is discussed in the presence of leptonic CP violation. We assume that both the solar scale and Ue3U_{e3} are zero at a high scale and the weak radiative corrections generate them. It is shown that all leptonic mass matrices satisfying these requirements lead to a unique prediction Δcos2θ4δτsin2θAmee2\Delta_{\odot} \cos 2\theta_{\odot}\approx 4 \delta_\tau \sin^2 \theta_A |m_{ee}|^2 for the solar scale in terms of the radiative correction parameter δτ\delta_\tau, the physical solar (atmospheric) mixing angles θodot(θA)\theta_{odot} (\theta_A) and the Majorana neutrino mass meem_{ee} probed in neutrinoless double beta decay. This relation is independent of the mixing matrix and CP-violating phases at the high scale. The presence of CP-violating phases leads to dilution in the solar mixing angle defined at the high scale. Because of this, bi-maximal mixing pattern at the high energy leads to large but non-maximal solar mixing in the low-energy theory. An illustrative model with this feature is discussed.Comment: 15 pages, including a postscript figur
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