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Register a new userExploring Neutrino Masses and Mixing in the Seesaw Model with $L_e - L_tau$ Gauged Symmetry
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In this work, we consider the implementation of $U(1)_{L_e-L_tau}$ gauge symmetry to study the neutrino phenomenology within the framework of type-(I+II) seesaw. The model involves three right-handed neutrinos, a scalar singlet along with a scalar triplet in addition to the standard model particle spectrum. The neutrino mass matrix is found to acquire a simple texture two-zero structure and thus, turns out to be quite helpful in explaining the neutrino oscillation parameters and also accommodating the effective electron neutrino mass ($m_{ee}$) in neutrinoless double beta decay. We also briefly discuss the lepton flavor violating $tau$ decays $tau to e gamma$ and $tau to mu bar mu mu$ in this model.
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The ANITA experiment has registered two anomalous events that can be interpreted as $ u_tau$ or $bar{ u}_tau$ with a very high energy of $mathcal{O}(0.6)$~EeV emerging from deep inside the Earth. At such high energies, the Earth is opaque to neutrinos so the emergence of these neutrinos at such large zenith angles is a mystery. In our paper, we present a model that explains the two anomalous events through a $L_e -L_tau$ gauge interaction involving two new Weyl fermions charged under the new gauge symmetry. We find that, as a bonus of the model, the lighter Weyl fermion can be a dark matter component. We discuss how the ANITA observation can be reconciled with the IceCube and Auger upper bounds. We also demonstrate how this model can be tested in future by collider experiments.
The latest measurements of the anomalous muon magnetic moment $a^{}_mu equiv (g^{}_mu - 2)/2$ show a $4.2sigma$ discrepancy between the theoretical prediction of the Standard Model and the experimental observations. In order to account for such a discrepancy, we consider a possible extension of the type-(I+II) seesaw model for neutrino mass generation with a gauged $L^{}_mu - L^{}_tau$ symmetry. By explicitly constructing an economical model with only one extra scalar singlet, we demonstrate that the gauge symmetry $U(1)^{}_{L^{}_mu - L^{}_tau}$ and its spontaneous breaking are crucially important not only for explaining the muon $(g - 2)$ result but also for generating neutrino masses and leptonic flavor mixing. Various phenomenological implications and experimental constraints on the model parameters are also discussed.
A generalized inverse seesaw model, in which the 9x9 neutrino mass matrix has vanishing (1,1) and (1,3) submatrices, is proposed. This is similar to the universal two-zero texture which gives vanishing (1,1) and (1,3) elements of the 3x3 mass matrices in both the charged lepton and neutrino sectors. We consider the Z_6 x Z_6 group to realize such texture zeros. We study this generalized inverse seesaw model systematically and derive the seesaw formula for the 3x3 mass matrix of three active neutrinos. We also analyze the universal two-zero texture in the general case and propose two ansatze to reduce the number of free parameters. Taking account of the new result of theta_{13} from the Daya Bay experiment, we constrain the parameter space of the universal two-zero texture in the general case and in the two ansatze, respectively. We find that one of the ansatze works well.
We present the $D_4times Z_2$ flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed.
We discuss neutrino mass and mixing in the framework of the classic seesaw mechanism, involving right-handed neutrinos with large Majorana masses, which provides an appealing way to understand the smallness of neutrino masses. However, with many input parameters, the seesaw mechanism is in general not predictive. We focus on natural implementations of the seesaw mechanism, in which large cancellations do not occur, where one of the right handed neutrinos is dominantly responsible for the atmospheric neutrino mass, while a second right-handed neutrino accounts for the solar neutrino mass, leading to an effective two right-handed neutrino model. We discuss recent attempts to predict lepton mixing and CP violation within such natural frameworks, focussing on the Littlest Seesaw and its distinctive predictions.
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