We study a type I seesaw model of neutrino masses within the framework of A 4 flavor symmetry.Incorporating the presence of both singlet and triplet flavons under A 4 symmetry, we construct the leptonic mass matrices involved in type I seesaw mechanism. We then construct the light neutrino mass matrix using the 3σ values of neutrino oscillation parameters keeping the presently undetermined parameters namely, the lightest neutrino mass m lightest , one Dirac CP phase δ and two Majorana phases α, β as free parameters. Comparing the mass matrices derived using A 4 parameters as well as light neutrino parameters, we then evaluate all the A 4 parameters in terms of light neutrino parameters. Assuming some specific vacuum alignments of A 4 triplet flavon field, we then numerically evaluate all the free parameters in the light neutrino sector, using which we also find out the remaining A 4 parameters. We then use the numerical values of these parameters to calculate baryon asymmetry through the mechanism of leptogenesis. We not only constrain the A 4 vacuum alignments from the requirement of successful leptogenesis, but also constrain the free parameters in the light neutrino sector (m lightest , δ, α, β) to certain range of values. These values can be tested in ongoing and future neutrino experiments providing a way to discriminate between different possible A 4 vacuum alignments discussed in this work.

We study the possibility of connecting leptonic Dirac CP phase δ, lightest neutrino mass and baryon asymmetry of the Universe within the framework of a model where both type I and type II seesaw mechanisms contribute to neutrino mass. Type I seesaw gives rise to Tri-Bimaximal (TBM) type neutrino mixing whereas type II seesaw acts as a correction in order to generate non-zero θ 13 .We derive the most general form of type II seesaw mass matrix which can not only give rise to correct neutrino mixing angles but also can generate non-trivial value of δ. Considering both the cases where type II seesaw is sub-leading and is equally dominant compared to type I seesaw, we correlate the type II seesaw term with δ and lightest neutrino mass. We further constrain the Dirac CP phase δ and hence the type II seesaw mass matrix from the requirement of producing the observed baryon asymmetry through the mechanism of leptogenesis.

We study all possible neutrino mass matrices with one zero element and two equal non-zero elements, known as hybrid texture neutrino mass matrices. In the diagonal charged lepton basis, we consider thirty nine such possible cases which are consistent with the latest neutrino data. Using the two constraints on neutrino mass matrix elements imposed by hybrid textures, we numerically evaluate the neutrino parameters like the lightest neutrino mass m lightest , one Dirac CP phase δ and two Majorana CP phases α, β by using the global fit 3σ values of three mixing angles and two mass squared differences. We then constrain this parameter space by using the cosmological upper bound on the sum of absolute neutrino masses given by Planck experiment. We also calculate the effective neutrino mass matrix for this region of parameter space which may have relevance in future neutrinoless double beta decay experiments. We finally discriminate between these hybrid texture mass matrices from the requirement of producing correct baryon asymmetry through type I seesaw leptogenesis. We also constrain the light neutrino parameter space as well as the lightest right handed neutrino mass from the constraint on baryon asymmetry of the Universe from Planck experiment.

We study a very specific type of neutrino mass and mixing structure based on the idea of Strong Scaling Ansatz (SSA) where the ratios of neutrino mass matrix elements belonging to two different columns are equal. There are three such possibilities, all of which are disfavored by the latest neutrino oscillation data. We focus on the specific scenario which predicts vanishing reactor mixing angle θ 13 and inverted hierarchy with vanishing lightest neutrino mass. Motivated by several recent attempts to explain non-zero θ 13 by incorporating corrections to a leading order neutrino mass or mixing matrix giving θ 13 = 0, here we study the origin of non-zero θ 13 as well as leptonic Dirac CP phase δ CP by incorporating two different corrections to scaling neutrino mass and mixing: one, where type II seesaw acts as a correction to scaling neutrino mass matrix and the other, with charged lepton correction to scaling neutrino mixing. Although scaling neutrino mass matrix originating from type I seesaw predicts inverted hierarchy, the total neutrino mass matrix after type II seesaw correction can give rise to either normal or inverted hierarchy. However, charged lepton corrections do not disturb the inverted hierarchy prediction of scaling neutrino mass matrix. We further discriminate between neutrino hierarchies, different choices of lightest neutrino mass and Dirac CP phase by calculating baryon asymmetry and comparing with the observations made by the Planck experiment.

We study the effects of Majorana neutrino phases in lepton flavor violation and the origin of matter-antimatter asymmetry through the mechanism of leptogenesis within the framework of a model where both type I and type II seesaw mechanisms can contribute to tiny neutrino masses. We parametrize the type I seesaw mass matrix by assuming it to give rise to a tri-bimaximal (TBM) type neutrino mixing which predicts θ 13 = 0. The type II seesaw mass matrix is then constructed in such a way that the necessary deviation from TBM mixing and the best fit values of neutrino parameters can be obtained when both type I and type II seesaw contributions are taken into account. Considering both subleading as well as equally dominating type II seesaw term, we first constrain the Majorana CP phases from the requirement of producing correct baryon asymmetry through leptogenesis and then incorporating the experimental bounds on lepton flavor violating decays μ → e + γ and μ → e + e + e.