Abstract
We study the possibility of generating non-zero reactor mixing angle $\theta_{13}$ and baryon asymmetry of the Universe within the framework of an $A_4$ flavour symmetric model. Using the conventional type I seesaw mechanism we construct the Dirac and Majorana mass matrices which give rise to the correct light neutrino mass matrix. Keeping the right handed neutrino mass matrix structure trivial so that it gives rise to a (quasi) degenerate spectrum of heavy neutrinos suitable for resonant leptogenesis at TeV scale, we generate the non-trivial structure of Dirac neutrino mass matrix that can lead to the light neutrino mixing through type I seesaw formula. Interestingly, such a setup naturally leads to non-zero $\theta_{13}$ due to the existence of anti-symmetric contraction of the product of two triplet representations of $A_4$. Such antisymmetric part of triplet products usually vanish for right handed neutrino Majorana mass terms, leading to $\mu-\tau$ symmetric scenarios in the most economical setups. We constrain the model parameters from the requirement of producing the correct neutrino data as well as baryon asymmetry of the Universe for right handed neutrino mass scale around TeV. The $A_4$ symmetry is augmented by additional $Z_3 \times Z_2$ symmetry to make sure that the splitting between right handed neutrinos required for resonant leptogenesis is generated only by next to leading order terms, making it naturally small. We find that the inverted hierarchical light neutrino masses give more allowed parameter space consistent with neutrino and baryon asymmetry data.
Highlights
Observations of tiny but nonzero neutrino mass and large leptonic mixing [1,2,3,4,5,6,7] have been one of the most compelling evidences suggesting the presence of beyond standard model (BSM) physics
Following the procedures outlined in the previous section, we first randomly generate the light neutrino parameters in their 3σ range [8] and for each set of values, we calculate the model parameters a, b, c, d using four equations
We have studied an extension of the standard model by discrete flavor symmetry A4 × Z3 × Z2 that can simultaneously explain the correct neutrino oscillation data and the observed baryon asymmetry of the Universe
Summary
Observations of tiny but nonzero neutrino mass and large leptonic mixing [1,2,3,4,5,6,7] have been one of the most compelling evidences suggesting the presence of beyond standard model (BSM) physics. In the conventional type I seesaw mechanism for example, the heavy right-handed neutrino decay generates the required lepton asymmetry that depends upon the scale of righthanded neutrino mass, and on the leptonic CP violation, which can be probed at ongoing oscillation experiments. If we generate the nontrivial leptonic mixing from a nontrivial right-handed neutrino mixing, like in the Altarelli-Feruglio-type models [18], such an antisymmetric term vanishes due to Majorana nature of this mass term This is not true in the case of the Dirac mass term, resulting in a nontrivial μ − τ symmetry breaking structure in the most general case.
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