T2K indication of relatively large θ_(13) and a natural perturbation to the democratic neutrino mixing pattern

The T2K Collaboration has recently reported a remarkable indication of the υμ＋ υe oscillation which is consistent with a relatively large value of θ13 in the three-flavor neutrino mixing scheme. We show that it is possible to account for such a result of θ13 by introducing a natural perturbation to the democratic neutrino mixing pattern, without or with CP violation. A testable correlation between θ13 and θ23 is predicted in this ansatz. We also discuss the Wolfenstein-like parametrization of neutrino mixing, and comment on other possibilities of generating sufficiently large θ13 at the electroweak scale.

A non-renormalizable B-L model with Q_(4)×Z_(4)×Z_(2) flavor symmetry for cobimaximal neutrino mixing

We construct a non-renormalizable gauge B-L model based on Q_(4)×Z_(4)×Z_(2) symmetry that successfully explains the cobimaximal lepton mixing scheme.Small active neutrino masses and both neutrino mass hierarchies are produced via the type-I seesaw mechanism at the tree-level.The model is predictive;hence,it reproduces the cobimaximal lepton mixing scheme,and the reactor neutrino mixing angle θ_(13) and the solar neutrino mixing angle θ_(12) can obtain best-fit values from recent experimental data.Our model also predicts the effective neut-rino mass parameters of mβ∈(8.80,9.05)meV and〈m_(ee)〉∈(3.65,3.95)meV for normal ordering(NO)and mβ ∈(49.16,49.2 l)meV and(mce)∈(48.59,48.67)meV for inverted ordering(IO),which are highly consistent with recent experimental constraints.

Determining the Neutrino Mass Eigenstates and the Effective Majorana Mass

This paper aims at solving several open questions in current neutrino physics: the neutrino mass hierarchy, the Dirac CP violating phase, the absolute mass of neutrinos, the nature of neutrinos (Dirac or Majorana), the Majorana matrix and the absolute value of the effective Majorana neutrino mass. In the research presented in this paper, we have shown that the precise definition of the mass splittings between neutrino mass eigenstates, done in the latest analysis of experimental data, can be of crucial importance for defining the nature of neutrino mass hierarchy. The Standard Model has three generations of fundamental matter particles. Three generations of the charged lepton mass show a hierarchical structure: mτ > mμ > me. Owing to that, there is a belief and it is considered that neutrinos may follow such hierarchical structure. In our calculations, we have also included the latest data obtained, based on the processing of measurement results, which showed that even with such data, obtained results favor the normal neutrino mass hierarchy. As for the individual neutrino mass calculated in this paper, in today’s neutrino physics it is only known that neutrino mass scale is bounded only from above, and both the Dirac and the Majorana character of neutrinos are compatible with all observations. Among some of the questions resolved in this paper, which are related to the properties of neutrinos, a positive answer was also given to the question of whether light neutrinos are self-conjugate particles or not.

A simplest seesaw model of the TM1 and μ-τ reflection symmetries for the neutrino masses and leptogenesis

In this paper,following the Occam’s razor principle,we have put forward a very simple form of the Dirac neutrino mass matrix M_(D) in the minimal seesaw model with the right-handed neutrino mass matrix being diagonal M_(R)=diag(M_(1),M_(2));it has one texture zero and only contains three real parameters,whose values can be determined from the neutrino oscillation experimental results.Such a model leads to a neutrino mass matrix M_(v)≃-M_(D)M_(R)^(-1)M_(D)^(T)that obeys the TM1 and μ-τ reflection symmetries simultaneously.In this way all the lepton flavor mixing parameters except for θ_(13) are predicted;the value of θ_(12) is predicted by the TM1 symmetry,while those of θ_(23),δ,ρ and σ by the μ-τ reflection symmetry.And the neutrino masses are predicted to be of the NO case with m_(1)=0,for which all three light neutrino masses will be pinned down with the help of the experimental results for the neutrino mass squared differences.For these results,the effective Majorana neutrino mass∣(M_(ν))_(ee)∣that controls the rate of the neutrinoless double beta decay is predicted to be 1.6 or 3.8 meV in the case of σ=0 or π/2.We have also studied the implications of the model for leptogenesis.It turns out that only in the two-flavor leptogenesis regime(which holds in the temperature range 10^(9)-10^(12) GeV)can leptogenesis have a chance to be successful.And a successful leptogenesis can be achieved at M_(1)≃1.2×10^(11) GeV in the case of σ=π/2,but not in the case of σ=0.

Is the magic texture of Majorana neutrinos immanent in Dirac nature?

Magic textures are successful candidates of the correct texture for Majorana neutrinos.In this study,we demonstrate that several types of magic textures of Majorana neutrinos are approximately immanent in the flavor mass matrix of Dirac neutrinos.In addition,the normal mass ordering of Dirac neutrino masses is slightly preferable to inverted mass ordering in the context of magic textures.

Linear seesaw model with T7 symmetry for neutrino mass and mixing

We propose a low-scale Standard Model extension with T_(7)×Z_(4)×Z_(3)×Z_(2) symmetry that can successfully explain observed neutrino oscillation results within the 3σrange.Small neutrino masses are obtained via the linear seesaw mechanism.Normal and inverted neutrino mass orderings are considered with three lepton mixing angles in their experimentally allowed 3σranges.The model provides a suitable correlation between the solar and reactor neutrino mixing angles,which is consistent with the TM2 pattern.The prediction for the Dirac phase isδCP∈(295.80,330.0)°for both normal and inverted orderings,including its experimentally maximum value,while those for the two Majorana phases areη1∈(349.60,356.60)°,η2=0 for normal ordering andη1∈(3.44,10.37)°,η2=0 for inverted ordering.In addition,the predictions for the effective neutrino masses are consistent with the pre sent experimental bounds.

Multiscalar B-L extension based on S_(4)flavor symmetry for neutrino masses and mixing

A multiscalar and nonrenormalizable B-L extension of the standard model(SM)with S_(4)symmetry which successfully explains the recently observed neutrino oscillation data is proposed.The tiny neutrino masses and their hierarchies are generated via the type-I seesaw mechanism.The model reproduces the recent experiments of neutrino mixing angles and Dirac CP violating phase in which the atmospheric angle(θ_(23))and the reactor angle(θ_(13))get the best-fit values while the solar angle(θ_(12))and Dirac CP violating phase(δ)are in 3σrange of the best-fit value for the normal hierarchy(NH).For the inverted hierarchy(IH),θ13 gets the best-ft value andθ_(23)together withδare in the lσrange,whileθ12 is in 3δrange of the best-fit value.The effective neutrino masses are pre-dicted to be(m_(ee))=6.81 meV for the NH and(m_(ee))=48.48 meV for the IH,in good agreement with the most re-cent experimental data.

NEUTRINO MASS,MIXING,AND OSCILLATIONS

Updated May 2014 by K. Nakamura （Kavli IPMU （WPI）, U. Tokyo, KEK）, and S.T. Petcov （SISSA/INFN Trieste, Kavli IPMU （WPI）, U. Tokyo, Bulgarian Academy of Sciences）.

Improved measurement of electron antineutrino disappearance at Daya Bay

We report an improved measurement of the neutrino mixing angle θ13 from the Daya Bay Reactor Neutrino Experiment. We exclude a zero value for sin22θ13 with a significance of 7.7 standard deviations. Electron antineutrinos from six reactors of 2.9 GWm th were detected in six antineutrino detectors deployed in two near （flux-weighted baselines of 470 m and 576 m） and one far （1648 m） underground experimental halls. Using 139 days of data, 28909 （205308） electron antineutrino candidates were detected at the far hall （near halls）. The ratio of the observed to the expected number of antineutrinos assuming no oscillations at the far hall is 0.944± 0.007（stat.） ± 0.003（syst.）. An analysis of the relative rates in six detectors finds sin22θ13=0.089± 0.010（stat.）±0.005（syst.） in a three-neutrino framework.

Friedberg-Lee neutrino model with μ–τ reflection symmetry

In this letter,we make an attempt to embed theμ–τreflection symmetry(which predicts maximal atmospherical mixing angle and Dirac CP phase)in the Friedberg-Lee neutrino model(which employs a translational flavor symmetry and keeps one neutrino mass vanishing)and study the consequences of such a combination.

Implications of fermionic dark matter on recent neutrino oscillation data

We investigate flavor phenomenology and dark matter in the context of the scotogenic model.In this model,the neutrino masses are generated through radiative corrections at the one-loop level.Considering the neutrino mixing matrix to be of tri-bimaximal form with additional perturbations to accommodate the recently observed nonzero value of the reactor mixing angle θ（13）,we obtain the relation between various neutrino oscillation parameters and the model parameters.Working in a degenerate heavy neutrino mass spectrum,we obtain light neutrino masses obeying the normal hierarchy and also study the relic abundance of fermionic dark matter candidates,including coannihilation effects.A viable parameter space is thus obtained,consistent with neutrino oscillation data,relic abundance and various lepton flavor violating decays such as 1α→1（βγ） and 1α→31β.

Overview on neutrinos and the Daya Bay experiment

Neutrinos are elementary particles in the Standard Model. Neutrino oscillation is a quantum mechanical phenomenon beyond the Standard Model. Neutrino oscillation can be described by two independent mass-squared differences △m21^2, △m31^2 （or △m32^2） and a 3× 3 unitary matrix, containing three mixing angles θ12, θ23, θ13, and one charge-parity （CP） phase. θ12 is about 34° and determined by solar neutrino experiments and the reactor neutrino experiment KamLAND. θ23 is about 45° and determined by atmospheric neutrino experiments and accelerator neutrino experiments. 013 can be measured by either accelerator or reactor neutrino experiments. On Mar. 8, 2012, the Daya Bay Reactor Neutrino Experiment reported the first observation of non-zero 013 with 5.2 standard deviations. In June, with 2.5× previous data, Daya Bay improved the measurement of sin2 2013 = 0.089 ± 0.010（stat）± 0.005（syst）.

Earthquake forecast via neutrino tomography

We discuss the possibility of forecasting earthquakes by means of （anti）neutrino tomography. Antineutrinos emitted from reactors are used as a probe. As the antineutrinos traverse through a region prone to earthquakes, observable variations in the matter effect on the antineutrino oscillation would provide a tomography of the vicinity of the region. In this preliminary work, we adopt a simplified model for the geometrical profile and matter density in a fault zone. We calculate the survival probability of electron antineutrinos for cases without and with an anomalous accumulation of electrons which can be considered as a clear signal of the coming earthquake, at the geological region with a fault zone, and find that the variation may reach as much as 3% for νˉe emitted from a reactor. The case for a νe beam from a neutrino factory is also investigated, and it is noted that, because of the typically high energy associated with such neutrinos, the oscillation length is too large and the resultant variation is not practically observable. Our conclusion is that with the present reactor facilities and detection techniques, it is still a difficult task to make an earthquake forecast using such a scheme, though it seems to be possible from a theoretical point of view while ignoring some uncertainties. However, with the development of the geology, especially the knowledge about the fault zone, and with the improvement of the detection techniques, etc., there is hope that a medium-term earthquake forecast would be feasible.

Neutrino masses,cosmological inflation and dark matter in a variant U(1)B-L model with type II seesaw mechanism

In this study,we implemented the type Ⅱ seesaw mechanism into the framework of the U(l)B-L gauge model.To achieve this,we added a scalar triplet,A,to the canonical particle content of the U(l)B-Lgauge model.By imposing that the U(l)B-L gauge symmetry be spontaneously broken at TeV scale,we show that the type Ⅱ seesaw mechanism is realized at an intermediate energy scale,more precisely,at approximately 109 GeV.To prevent heavy right-handed neutrinos from disturbing the mechanism,we evoke a Z2 discrete symmetry.Interestingly,as a result,we have standard neutrinos with mass around eV scale and right-handed neutrinos with mass in TeV scale,with the lightest one fulfilling the condition of dark matter.We developed all of these in this study.In addition,we show that the neutral component of Δ may perform unproblematic non-minimal inflation with loss of unitarity.

Testing lepton f lavor universality in terms of BESⅢ and charm-tau factory data

The recent measurements on Rκ and Rπ imply that there exists a possible violation of the leptonic flavor universality which is one of the cornerstones of the Standard Model. It is suggested that a mixing between sterile and active neutrinos might induce such a violation. In this work we consider the scenarios with one or two sterile neutrinos to explicitly realize the data while the constraints from the available experiments have been taken into account. Moreover, as indicated in literature, the deviation of the real PMNS matrix from the symmetric patterns may be due to a μ-τ asymmetry, therefore the measurements on RD（Ds）eμ=F（D（Ds）→e＋νe）/Г（D（Ds）→μ＋νμ） and RD（Ds）μτ=Г（D（Ds）→μ＋νμ）Г（D（Ds）→ι＋ντ） （and for some other heavy mesons B± and Bc etc.） may shed more light on the physics responsible for the violation of the leptonic flavor universality. The data of BESⅢ are available to test the universality and that of future charm-tau factories will provide more accurate information. In this work, we will discuss RD（Ds）eμ and RD（Ds）μτ in detail and also briefly consider the cases for B± and Bc.