The implications of a large value of the effective Majorana neutrino mass for a class of two texture zero neutrino mass matrices have been studied in the flavor basis. It is found that these textures predict near maximal atmospheric neutrino mixing angle in the limit of large effective Majorana neutrino mass. It is noted that this prediction is independent of the values of solar and reactor neutrino mixing angles. We present the symmetry realization of these textures using the discrete cyclic group Z3. It is found that the texture zeros realised in this work remain stable under renormalization group running of the neutrino mass matrix from the seesaw scale to the electroweak scale, at one loop level.
We study the implications of the existence of two equalities between the elements or cofactors of the neutrino mass matrix. There are sixty five structures of this type for each case. Phenomenological implications for unknown parameters like the effective Majorana mass of the electron neutrino and CP-violating phases are examined for the viable cases. To illustrate how such forms of the neutrino mass matrices may be realized, we also present a simple A 4 model for one of the classes in each case. * dev5703@yahoo.com †
We perform a systematic study of neutrino mass matrices having a vanishing cofactor and an equality between two cofactors of the mass matrix. Such texture structures of the effective neutrino mass matrix arise from type-I seesaw mechanism when the Dirac neutrino mass matrix is diagonal with two equal elements and the right-handed Majorana neutrino mass matrix has hybrid textures with one equality of matrix elements and one zero matrix element. For three righthanded neutrinos there are sixty possible hybrid textures out of which only six are excluded by the present experimental data. We show that such textures can be derived using discrete symmetries. The predictions of experimentally allowed textures are examined for unknown parameters such as the effective Majorana mass of the electron neutrino and the Dirac-type CP-violating phase. * dev5703@yahoo.com †
In the flavor basis there are seven cases of two vanishing minors in the neutrino mass matrix which can accommodate the present neutrino oscillation data including the recent T2K data. It is found that two of these cases, namely B 5 and B 6 predict near maximal atmospheric neutrino mixing in the limit of large effective neutrino mass. This feature remains irrespective of the values of solar and reactor mixing angles. A non-zero reactor mixing angle is naturally accommodated in these textures. * dev5703@yahoo.com † shiroberts 1980@yahoo.co.in ‡
We propose new mixing schemes for (3+1) neutrinos which describe mixing among active-active and active-sterile neutrinos. The mixing matrix in these mixing schemes can be factored into a zeroth order flavor symmetric part and another part representing small perturbations needed for generating non-zero Ue3, nonmaximal θ23, CP violation and active-sterile mixing. We find interesting correlations amongst various neutrino mixing angles and, also, calculate the parameter space for various parameters. IntroductionThe discovery of massive neutrinos by Super-Kamiokande experiment [1] in the year 1998 has paved the way for new physics beyond the Standard Model (BSM) of particle physics. Various neutrino oscillation experiments in the last two decades have measured the three neutrino mixing angles and two (atmospheric |∆m 2 23 | and solar ∆m 2 21 ) mass splittings rather precisely. However, several anomalies at Short Base Line (SBL) neutrino experiments indicate eV scale mass splitting. These anomalies were first reported by LSND experiment [2] in their anti-neutrino flux measurements and, subsequently, confirmed by MiniBooNE experiment [3] in both the neutrino and antineutrino modes. The recent MiniBooNE data [4] also support these anomalies. In addition, reactor experiments [5] and gallium solar neutrino experiments [6] strongly support these anomalies. A possible explanation of these anomalies would require, at least, one eV scale mass eigenstate in the neutrino sector and the decay width of Z boson would require the fourth neutrino state to be sterile. The recent global analysis [7] of neutrino oscillations in the presence of eV-scale sterile neutrinos, supports the explanation of reactor anomaly in terms of sterile neutrino oscillations in 3+1 scenario but disfavour sterile neutrino explanation of LSND anomaly.Reactor neutrino data favour sterile neutrino oscillation with ∆m 2 41 ≈ 1.3eV 2 and |U e4 | ≈ 0.1 at the 3σ confidence level (CL) [7,8].The recent Planck data [9] limit the effective number of relativistic degrees of freedom to N ef f = 3.15 ± 0.23 (Planck TT+lowP+BAO) at 95% CL and the sum of neutrino masses to be m ν ≤ 0.23 eV at the same confidence level. This is consistent with the bound given by the standard model of cosmology: N ef f = 3.046.Although the cosmological bounds and latest Planck data disfavour the existence of eV scale sterile neutrinos, * sdev@associates.iucaa.in † raj.physics88@gmail.com ‡
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