The generic predictions of two-texture zero neutrino mass matrices in the flavor basis have been examined especially in relation to the degeneracies between mass matrices within a class and interesting constraints on the neutrino parameters have been obtained. It is shown that the knowledge of the octant of θ 23 , the sign of cos δ and neutrino mass hierarchy can be used to lift these degeneracies. IntroductionMass matrices provide important tools for the investigation of the underlying symmetries and the resulting dynamics. The first step in this direction is the reconstruction of the neutrino mass matrix in the flavor basis. However, the reconstruction results in a large variety of possible structures of mass matrices depending strongly on the mass scale, mass hierarchy and the Majorana phases. However, the relatively weak dependence on some oscillation parameters (θ 23 and δ) results in the degeneracy of possible neutrino mass matrices. The mass matrix for Majorana neutrinos contains nine physical parameters including the three mass eigenvalues, three mixing angles and the three CP-violating phases. The two squared-mass differences (∆m 2 12 and ∆m 2 13 ) and the two mixing angles (θ 12 and θ 23 ) have been measured in solar, atmospheric and reactor experiments. The third mixing angle θ 13 and the Dirac-type CP-violating phase δ are expected to be measured in the forthcoming neutrino oscillation experiments. The possible measurement of the effective Majorana mass in neutrinoless double β decay searches will provide an additional constraint on the remaining three neutrino parameters viz. the neutrino mass scale and two Majorana-type CP-violating phases. While * dev5703@yahoo.com †

The generic predictions of two-texture zero neutrino mass matrices of class A in the flavor basis have been reexamined especially in relation to the degeneracy between mass matrices of types A 1 and A 2 and interesting constraints on the neutrino parameters have been obtained. It is shown that the octant of θ 23 and the quadrant of the Diractype CP-violating phase δ can be used to lift this degeneracy.Mass matrices provide important tools for the investigation of the underlying symmetries and the resulting dynamics. The first step in this direction is the reconstruction of the neutrino mass matrix in the flavor basis. However, the reconstruction results in a large variety of possible structures of mass matrices depending strongly on the mass scale, mass hierarchy and the Majorana phases. However, the relatively weak dependence on some oscillation parameters (θ 23 and δ) results in the degeneracy of possible neutrino mass matrices since all the parameters are not known at present. The mass matrix for Majorana neutrinos contains nine physical parameters including the three mass eigenvalues, three mixing angles and the three CP-violating phases. The two squared-mass differences (∆m 2 21 and ∆m 2 32 ) and the two mixing angles (θ 12 and θ 23 ) have been measured in solar, atmospheric and reactor experiments. The third mixing angle θ 13 and the Dirac-type CP-violating phase δ are expected to be measured in the forthcoming neutrino oscillation experiments. The possible measurement of the effective Majorana mass in neutrinoless double β decay searches will provide an additional constraint on the remaining three neutrino parameters viz. the neutrino mass scale and two Majorana CP violating phases. While the neutrino mass scale will be determined by the direct beta decay searches and cosmological observations, the two Majorana phases will not be uniquely determined even if the absolute neutrino mass scale is known. Under the circumstances, it is natural to employ other theoretical inputs * dev5703@yahoo.com † sanjeev3kumar@yahoo.co.in ‡ s 7verma@yahoo.co.in § shiroberts 1980@yahoo.co.in 1 for the reconstruction of the neutrino mass matrix. Several proposals have been made in the literature to restrict the form of the neutrino mass matrix and to reduce the number of free parameters which include presence of texture zeros [1,2,3,4], requirement of zero determinant [5,6] and the zero trace condition [7] to name a few. However, the current neutrino oscillation data are consistent only with a limited number of texture schemes [1,2,3,4]. In particular, the current neutrino oscillation data disallow all neutrino mass matrices with three or more texture zeros in the flavor basis. Out of the fifteen possible neutrino mass matrices with two texture zeros, only seven are compatible with the current neutrino oscillation data. The seven allowed two texture zero mass matrices have been classified into three categories. The two class A matrices of the types A 1 and A 2 give hierarchical neutrino masses. The class B matrices of ...

We study the implications of the simultaneous existence of a texture zero and a vanishing minor in the neutrino mass matrix. There are thirty six possible texture structures of this type, twenty one of which reduce to two texture zero cases which have, already, been extensively studied. Of the remaining fifteen textures only six are allowed by the current data. We examine the phenomenological implications of the allowed texture structures for Majorana type CP-violating phases, 1-3 mixing angle and Dirac type CP-violating phase. All these possible textures can be generated through the seesaw mechanism and realized in the framework of discrete abelian flavor symmetry. We present the symmetry realization of these texture structures. * Electronic address: dev5703@yahoo.com †

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.

For Majorana or Dirac neutrinos, using Fritzsch-like texture 4 zero mass matrices with parallel texture structures for the charged leptons and the Dirac neutrino mass matrix (M_{\nu D}), detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenarios of neutrino masses have been carried out. The inverted hierarchy as well as degenerate scenarios seem to be ruled out at 3 \sigma C.L. for both Majorana and Dirac neutrinos. For normal hierarchy, Jarlskog's rephasing invariant parameter J, the CP violating Dirac-like phase \delta and the effective neutrino mass m_{ee} have been calculated. For this case, lower limits of m_{\nu_1} and \theta_{13} would have implications for the nature of neutrinos.Comment: 15 pages, 3 figures, minor changes in figures and tex

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 present a comprehensive phenomenological analysis of the allowed hybrid textures of neutrinos. Out of a total of sixty hybrid textures with one equality between the elements of neutrino mass matrix and one texture zero only twenty three are found to be viable at 99% C.L. whereas the earlier analysis found fifty four to be viable. We examine the phenomenological implications of the allowed hybrid textures including Majorana type CP-violating phases, 1-3 mixing angle and Dirac type CP-violating phase, δ. We, also, obtain lower bound on effective Majorana mass for all the allowed hybrid textures.

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 †