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Register a new userGenerating $theta_{13}$ from sterile neutrinos in $mu - tau$ symmetric models
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The smallness of the $theta_{13}$ mixing angle as observed in neutrino oscillation experiments can be understood through an approximated $mu - tau$ exchange symmetry in the neutrino mass matrix. Using recent oscillation neutrino data, but assuming no textit{CP} violation, we study $mu-tau$ breaking parameter space to establish the conditions under which such a breaking could have a perturbative origin. According to the so-obtained conditions, we suggest that a sterile neutrino, matching LSND/MiniBooNE neutrino oscillation results, could provide the necessary ingredients to properly fix atmospheric and $theta_{13}$ mixing angles to observable values, without exceeding the sterile neutrino fraction bound in solar oscillations. In such a scenario, we analyze the general effect of a fourth neutrino on the prediction for the effective $m_{ee}$ majorana mass parameter.
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Solar neutrino experiments have yet to see directly the transition region between matter-enhanced and vacuum oscillations. The transition region is particularly sensitive to models of non-standard neutrino interactions and propagation. We examine several such non-standard models, which predict a lower-energy transition region and a flatter survival probability for the ^{8}B solar neutrinos than the standard large-mixing angle (LMA) model. We find that while some of the non-standard models provide a better fit to the solar neutrino data set, the large measured value of theta_{13} and the size of the experimental uncertainties lead to a low statistical significance for these fits. We have also examined whether simple changes to the solar density profile can lead to a flatter ^{8}B survival probability than the LMA prediction, but find that this is not the case for reasonable changes. We conclude that the data in this critical region is still too poor to determine whether any of these models, or LMA, is the best description of the data.
Distinguishing the Dirac and Majorana nature of neutrinos remains one of the most important tasks in neutrino physics. By assuming that the $tau^- to pi^- mu^- e^+ u$ (or $bar{ u}$) decay is resonantly enhanced by the exchange of an intermediate mass sterile neutrino $N$, we show that the energy spectrum of emitted pions and muons can be used to easily distinguish between the Dirac and Majorana nature of $N$. This method takes advantage of the fact that the flavor of light neutrinos is not identified in the tau decay under consideration. We find that it is particularly advantageous, because of no competing background events, to search for $N$ in the mass range $m_e + m_{mu} leqslant m_N leqslant m_{mu} + m_{pi}$, where $m_X$ denotes the mass of particle $X in { e, mu, pi, N }$.
We study the lepton flavor models with the flavor symmetry (Z_N times Z_N times Z_N)rtimes Z_3. Our models predict non-vanishing discrete values of theta_{13} as well as theta_{12} and theta_{23} depending on N. For certain values, our models realize the tri-bimaximal mixing angles with theta_{13}=0. For other values, our models provide with discrete deviation from the tri-bimaximal mixing angles.
Leptonic CP Violating Phase $ delta_{CP} $ in the light neutrino sector and leptogenesis via present matter antimatter asymmetry of the Universe entails each other. Probing CP violation in light neutrino oscillation is one of the challenging tasks today. The reactor mixing angle $ theta_{13} $ measured in reactor experiments, LBL, DUNE with high precision in neutrino experiments indicates towards the vast dimension of scope to detect $ delta_{CP} $. The correlation between leptonic Dirac CPV phase $ delta_{CP} $, reactor mixing angle $ theta_{13} $, lightest neutrino mass $ m_{1} $ and matter antimatter asymmetry of the Universe within the framework of $ mu-tau $ symmetry breaking assuming the type I seesaw dominance is extensively studied here. Small tiny breaking of the $ mu-tau $ symmetry allows a large Dirac CP violating phase in neutrino oscillation which in turn is characterised by awareness of measured value of $ theta_{13} $ and to provide a hint towards a better understanding of the experimentally observed near maximal value of $ u_{mu} - u_{tau} $ mixing angle $ theta_{23}simeq frac{pi}{4}$. Precise breaking of the $ mu-tau $ symmetry is achieved by adding a 120 plet Higgs to the 10 $+$ $bar{126}$ dimensional representation of Higgs. The estimated three dimensional density parameter space of lightest neutrino mass $ m_{1} $, $ delta_{CP} $, reactor mixing angle $ theta_{13} $, is constrained here for the requirement of producing the observed value of baryon asymmetry of the Universe through the mechanism of leptogenesis. Carrying out numerical analysis the allowed parameter space of $ m_{1} $, $ delta_{CP} $, $ theta_{13} $, is found out which can produce the observed baryon to photon density ratio of the Universe.
Light sterile neutrinos can be probed in a number of ways, including electroweak decays, cosmology and neutrino oscillation experiments. At long-baseline experiments, the neutral-current data is directly sensitive to the presence of light sterile neutrinos: once the active neutrinos have oscillated into a sterile state, a depletion in the neutral-current data sample is expected since they do not interact with the $Z$ boson. This channel offers a direct avenue to probe the mixing between a sterile neutrino and the tau neutrino, which remains largely unconstrained by current data. In this work, we study the potential of the DUNE experiment to constrain the mixing angle which parametrizes this mixing, $theta_{34}$, through the observation of neutral-current events at the far detector. We find that DUNE will be able to improve significantly over current constraints thanks to its large statistics and excellent discrimination between neutral- and charged-current events.
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