Radha Raman Gautam

Near maximal atmospheric mixing in neutrino mass matrices with two vanishing minors

Abstract 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.

Broken S-3 symmetry in the neutrino mass matrix and non-zero theta(13)

We study the effects of breaking S-3 symmetry in the neutrino mass matrix for the masses and mixing matrix of neutrinos. At zeroth order the model gives degenerate neutrino masses and accommodates tribimaximal mixing. We introduce perturbations in terms of a small and complex parameter. The perturbations are introduced in a manner such that the S-3 symmetry is broken by its elements in the same representation. Successive perturbations introduce mass splitting, sizable non-zero reactor mixing angle and CP violation. This scheme of breaking S-3 symmetry can reproduce a relatively large reactor mixing angle as suggested by the recent T2K results. The effective neutrino mass is predicted to be large which is testable in the ongoing and forthcoming neutrinoless double beta decay experiments

Neutrino Mass Matrices with a Texture Zero and a Vanishing Minor

We study the implications of the simultaneous existence of a texture zero and a vanishing minor in the neutrino mass matrix. There are 36 possible texture structures of this type, 21 of which reduce to two texture zero cases which have, already, been extensively studied. Of the remaining 15 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.

Parametrizing the Lepton Mixing Matrix in terms of Charged Lepton Corrections

We consider a parametrization of the lepton mixing matrix in which the deviations from maximal atmospheric mixing and vanishing reactor mixing are obtained in terms of small corrections from the charged lepton sector. Relatively large deviations for the reactor mixing angle from zero as indicated by T2K experiment can be obtained in this parametrization. We are able to further reduce the number of complex phases, thus, simplifying the analysis. In addition, we have obtained the sides of unitarity triangles and the vacuum oscillation probabilities in this parametrization. The Jarlskog rephasing invariant measure of CP violation at the leading order has a single phase difference which can be identified as Dirac-type CP violating phase in this parametrization.

Broken S 3 Symmetry in the Neutrino Mass Matrix

We explore the feasibility of the discrete flavor symmetry S3 to explain the pattern of neutrino masses and mixings. In the flavor basis, the neutrino mass matrix is taken to be invariant under S3 symmetry at the zeroth order. The effects of breaking S3 symmetry by matrices invariant under different S2 subgroups of S3 are studied. The resulting retrocirculant perturbation matrix leads to the perturbed S3 neutrino mass matrix having a trimaximal eigenvector as suggested by the solar neutrino data. It is found that after the third order perturbation the neutrino mixings only depend on the perturbation parameter and are consistent with the current experimental data leading to very small deviations from tribimaximal mixing. These perturbations in the S3 invariant neutrino mass matrix result in interesting interplay between the solar and the reactor neutrino mixing angles. We also get a strongly suppressed range of effective Majorana mass which lies well within the reach of the ongoing experiments.

Zero textures of the neutrino mass matrix from cyclic family symmetry

Abstract We present the symmetry realization of the phenomenologically viable Frampton–Glashow–Marfatia (FGM) two zero texture neutrino mass matrices in the flavor basis within the framework of the type ( I + II ) seesaw mechanism natural to SO(10) grand unification. A small Abelian cyclic symmetry group Z 3 is used to realize these textures except for class C for which the symmetry is enlarged to Z 4 . The scalar sector is restricted to the Standard Model (SM) Higgs doublet to suppress the flavor changing neutral currents. Other scalar fields used for symmetry realization are at the most two scalar triplets and, in some cases, a complex scalar singlet. Symmetry realization of one zero textures has, also, been presented.

Neutrino mass matrices with one texture zero and a vanishing neutrino mass

Assuming Majorana nature of neutrinos, we investigate the singular one texture zero neutrino mass matrices in the flavor basis. We find that for the normal mass ordering with

Neutrino Mass Matrices with Two Equalities Between the Elements or Cofactors

m_1=0

Near Maximal Atmospheric Neutrino Mixing in Neutrino Mass Models with Two Texture Zeros

, all the six one texture zero classes are now ruled out at 3

Parallel hybrid textures of lepton mass matrices

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