Many neutrino experiments in the last few years
have shown concrete evidence for neutrino mass and leptonic mixing; an indication of new physics beyond the standard model. In this thesis, we systematically study the flavor symmetry indicated by the low scale neutrino experiment data with the assumption that the seesaw mechanism is the reason for the light neutrino masses.
In the flavor basis, the testable exchange symmetry between muon neutrino and tau neutrino (\mu-\tau)isintroducedtoexplainthenearmaximalatmosphericmixingangleandvanishingreactormixingangle.Thissymmetrycanreducetheseesawparametersnaturallyandmakeitpossibletoconnectthebaryonasymmetryofouruniversetothelowscaleneutrinodataifleptogenesiscausesthebaryonasymmetry.WealsoshowthisleptonicsymmetrycanbeextendedtothequarksectorandpresentarealisticsupersymmetrySU(5)grandunificationmodel.Motivatedbysolarmixingangle\sin^2\theta_{\rm
solar}\simeq1/3,weembedthe\mu-\tausymmetryinanS3permutationsymmetryandobtainaso−calledtri−bimaximalmixingpattern.Westudythestabilityofthetextureunderradiativecorrections.ThisS3modelissoconstrainedthattheCP−violatingphasesofthelowscalemixingarethosegeneratingthebaryonasymmetrywithinleptongesis.Attemptingtounifythreefamiliesoffermionswithinthegrandunificationtheories,wetreatthreefamiliesoffermionsasthethreedimensionalirreduciblerepresentationofS4andbuildarealisticmodelbasedonSO(10)gaugegroup.Thismodelpredictsdegeneratearight−handedneutrinomassspectrum.Inthisthesis,wealsoaddresstheissueofthenaturalrealizationoftheseesawmechanisminthesupersymmetricminimalSO(10)$
model. We realize the type II seesaw dominance by invoking a warped
extra dimension, while keeping predictivity of the model