Abstract
We propose two different seesaw models namely, type I and inverse seesaw to realise light Dirac neutrinos within the framework of A4 discrete flavour symmetry. The additional fields and their transformations under the flavour symmetries are chosen in such a way that naturally predicts the hierarchies of different elements of the seesaw mass matrices in these two types of seesaw mechanisms. For generic choices of flavon alignments, both the models predict normal hierarchical light neutrino masses with the atmospheric mixing angle in the lower octant. Apart from predicting interesting correlations between different neutrino parameters as well as between neutrino and model parameters, the model also predicts the leptonic Dirac CP phase to lie in a specific range −π/3 to π/3. While the type I seesaw model predicts smaller values of absolute neutrino mass, the inverse seesaw predictions for the absolute neutrino masses can saturate the cosmological upper bound on sum of absolute neutrino masses for certain choices of model parameters.
Highlights
The observations of non-zero neutrino mass and large leptonic mixing have been confirmed by several neutrino experiments in the last two decades [1,2,3,4,5,6,7], three important issues related to neutrino physics are yet not settled
We look at the possibility of a flavour symmetric scenario for Dirac neutrinos within the well motivated A4 flavour symmetry group
We have studied two different seesaw scenarios for light Dirac neutrinos namely, type I and inverse seesaw within the framework of A4 flavour symmetry to explain lepton masses and mixing
Summary
The observations of non-zero neutrino mass and large leptonic mixing have been confirmed by several neutrino experiments in the last two decades [1,2,3,4,5,6,7], three important issues related to neutrino physics are yet not settled. Similar to the type I seesaw case, here we can naturally explain the hierarchy of different terms present in the inverse seesaw mass matrix In both of these models, the antisymmetric term arising out of the products of two A4 triplets plays a non-trivial role in generating the correct neutrino mixing. In some cases, the charged lepton mass matrix can be non-trivial and has an important contribution to lepton mixing Both of the discrete flavour symmetric constructions for type I and inverse seesaw mechanisms show highly predictive nature of the models for generic choices of flavon alignments.
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