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Register a new userCompatibility of $A_{4}$ Flavour Symmetric Minimal Extended Seesaw with $(3+1)$ Neutrino Data
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Motivated by the recent resurrection of the evidence for an eV scale sterile neutrino from the MiniBooNE experiment, we revisit one of the most minimal seesaw model known as the minimal extended seesaw that gives rise to a $3+1$ light neutrino mass matrix. We consider the presence of $A_4$ flavour symmetry which plays a non-trivial role in generating the structure of the neutrino mass matrix. Considering a diagonal charged lepton mass matrix and generic vacuum alignments of $A_4$ triplet flavons, we classify the resulting mass matrices based on their textures. Keeping aside the disallowed texture zeros based on earlier studies of $3+1$ neutrino textures, we categorise the remaining ones based on texture zeros, $mu-tau$ symmetry in the $3times3$ block and hybrid textures. After pointing out the origin of such $3+1$ neutrino textures to $A_4$ vacuum alignments, we use the latest $3+1$ neutrino oscillation data and numerically analyse the texture zeros and $mu-tau$ symmetric cases. We find that a few of them are allowed from each category predicting interesting correlations between neutrino parameters. We also find that all of these allowed cases prefer normal hierarchical pattern of light neutrino masses over inverted hierarchy.
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We propose a Standard Model extension with underlying A4 flavour symmetry where small Dirac neutrino masses arise from a Type-II seesaw mechanism. The model predicts the golden flavour-dependent bottom-tau mass relation, requires an inverted neutrino mass ordering and non-maximal atmospheric mixing angle. Using the latest neutrino oscillation global fit we derive restrictions on the oscillation parameters, such as a correlation between Dirac CP phase and the lightest neutrino mass.
We explore realizations of minimal flavour violation (MFV) for the lepton sector. We find that it can be realized within those seesaw models where a separation of the lepton number and lepton flavour violating scales can be achieved, such as type II and inverse seesaw models. We present in particular a simple implementation of the MFV hypothesis which differs in nature from those previously discussed. It allows to reconstruct the flavour structure of the model from the values of the light neutrino masses and mixing parameters, even in the presence of CP-violating phases. Experimentally reachable predictions for rare processes such as mu --> e gamma are given.
In this work, we present a comparative study of the three of the seesaw models, viz., type II, inverse and linear seesaw models, to investigate about light neutrino masses and mixings, flavour structure, neutrinoless double beta decay ($ 0 u beta beta $) and charged lepton flavour violation (cLFV) decay ($murightarrow egamma$). We consider the $ A_{4} $ flavour symmetry, while some other symmetries, like $U(1)_{X}$, $Z_4$ and $Z_5$ are also included to forbid unwanted terms in the Lagrangian. Taking into account the present experimental data for the known light neutrino parameters from recent global fit data, we compute the currently unknown neutrino parameters such as the lightest neutrino mass ($m_1$), CPV phase (Dirac and Majorana), and effective light neutrino mass in the neutrinoless double beta decay, by considering different VEV alignments of the triplet scalar flavon fields. We also elucidate on the octant of atmospheric neutrino mixing angle, $theta_{23}$, in the light of our predicted results. Finally, we present the region of parameter spaces of $m_1$, CPV phases, octant of $theta_{23}$ and effective mass measurable in of neutrino less double beta decay experiments, that can be tested in future experiments. We observe that the branching ratio of ($murightarrow egamma$) can help discriminate the three seesaw models. Further, the favoured Octant of the atmospheric mixing angle $theta_{23}$ changes with the VEV alignment of the triplet flavon field - i.e., the internal flavour structure of the neutrinos is reflected in their composition (mixing). The constant F determining the scale of flavour symmetry breaking, seesaw scale and coupling constants of the three seesaw models has also been computed, which puts a constraint among them allowed by the present experimental results.
We explore the possibility of a single generation of $keV$ scale sterile neutrino ($m_S$) as a dark matter candidate within the minimal extended seesaw (MES) framework and its influence in neutrinoless double beta decay ($0 ubetabeta$) study. Three hierarchical right-handed neutrinos were considered to explain neutrino mass. We also address baryogenesis via the mechanism of thermal leptogenesis considering the decay of the lightest RH neutrino to a lepton and Higgs doublet. A generic model based on $A_4times Z_4times Z_3$ flavor symmetry is constructed to explain both normal and inverted hierarchy mass pattern of neutrinos. Significant results on effective neutrino masses are observed in presence of sterile mass ($m_S$) and active-sterile mixing ($theta_{S}$) in $0 ubetabeta$. Results from $0 ubetabeta$ give stringent upper bounds on the active-sterile mixing matrix element. To establish sterile neutrino as dark matter within this model, we checked decay width and relic abundance of the sterile neutrino, which restricted sterile mass ($m_S$) within some definite bounds. Constrained regions on the CP-phases and Yukawa couplings are obtained from $0 ubetabeta$ and baryogenesis results. Co-relations among these observable are also established and discussed within this framework.
Motivated by the recent muon anomalous magnetic moment (g-2) measurement at FERMILAB and non-zero neutrino masses, we propose a model based on the $SU(3)_C times SU(3)_L times U(1)_X$ (3-3-1) gauge symmetry. The most popular 3-3-1 models in the literature require the presence of a scalar sextet to address neutrino masses. In our work, we show that we can successfully implement an one-loop linear seesaw mechanism with right-handed neutrinos, and vector-like fermions to nicely explain the active neutrino masses, and additionally reproduce the recent Muon g-2 result, in agreement with existing bounds.
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