The MSW mechanism for three neutrino generations and the solar neutrino puzzle

We analyse the ³⁷Cl experiment for three neutrino generations with arbitrary mixing angles in the adiabatic approximation and present the resulting ⁸B-neutrino energy spectrum.     

Experimental analysis of weak mixing angles between three or four quark generations

New data on weak quark decays and on weak heavy quark production are used to obtain the allowed ranges of elements of the quark mixing matrix for three or four generations of sequential quarks. The analysis yields allowed ranges for the three mixing angles in the six-quark case and for the six mixing angles in the eight-quark case.     

Oscillations of three generations of neutrinos and the solar neutrino problem

The resonant neutrino oscillations in matter are assumed to be responsible for the observed reduction in the capture rate for the ³⁷Cl detector. The expression of the probability that a solar v_e reaches the Earth as a v_e is given in the case of three generations. In the small mixing angle approximation, we describe all the regions of neutrino parameters which give rise to a capture rate of 2.1 SNU for ³⁷Cl and we give the corresponding prediction for the ⁷¹Ga detector.     

Coherent mixing in three and four quark generations

New dynamical mechanism of quark mass generations and mixing is demonstrated in the examples of three and four generations. In the framework of the new mixing pattern, called the coherent mixing, the CKM elements are predicted compatible with experimental data for three generations, and are strongly constrained for four generations.     

A simple modification of the maximal mixing scenario for three light neutrinos

We suggest a simple modification of the maximal mixing scenario (withS ₃ permutation symmetry) for three light neutrinos. Our neutrino mass matrix has smaller permutation symmetryS ₂(ν _μ ?ν _e ), and is consistent with all neutrino experiments except the³⁷Cl experiment. The resulting mass eigenvalues for three neutrinos arem ₁≈(2.55?1.27)×10^?3eV,m _2,3≈(0.71?1.43)eV for Δm _LSND ² =0.5?2.0eV². Then these light neutrinos can account for ～(2.4?4.8)% (6.2?12.4%) of the dark matter forh=0.8 (0.5). Our model predicts theν _μ →ν _τ oscillation probability in the range sensitive to the future experiments such as CHORUS and NOMAD.     

Domain of mixing angles in three flavor neutrino oscillations

We clarify the domain needed for the mixing angles in three flavor neutrino oscillations. By comparing the ranges of the transition probabilities as functions of the domains of the mixing angles, we show that it is necessary and sufficient to let all mixing angles be in . This holds irrespectively of any assumptions on the neutrino mass squared differences.     

Dirac and Majorana neutrinos in matter

We consider the matter effects on neutrinos moving in background on the basis of the corresponding quantum wave equations. Both Dirac and Majorana neutrino cases are discussed. The effects for Dirac neutrino reflection and trapping as well as neutrino—antineutrino annihilation and ν pair creation in matter at the interface between two media with different densities are considered. The spin light of neutrinos in matter is also discussed. The text was submitted by the authors in English.     

Phenomenological relations for quark and neutrino mixing angles

The most recent experimental data on quark and neutrino mixing angles are discussed. It is indicated that the results of the latest kaon-decay experiments are consistent with the unitarity condition for the first row of the Cabibbo-Kobayashi-Maskawa matrix if the currently available world-average value of the neutron lifetime is used to determine the element V _ud of this matrix. The quark mixing angles are calculated within the Fritzsch-Scadron-Delbourgo-Rupp phenomenological approach on the basis of values of the masses of light and heavy constituent quarks. The neutrino mixing angles are calculated to a high precision with the aid of the hypothesis that the quark and neutrino mixing angles are complementary. The results are compatible with experimental data.     

Resonant oscillations of massless neutrinos in matter

Oscillations of neutrinos propagating in matter do not require that neutrinos are massive, at a fundamental level. Even if neutrinos are massless as a consequence of an exact symmetry - such as total lepton number - they can oscillate into one another if the weak interaction has a small non-universal component, whose existence would signal physics beyond the standard model. The experimental constraints and theoretical plausibility of the mechanism are discussed. Coherent neutrino and antineutrino scattering could substantially affect the late thermal phase neutrino signal from a supernova explosion.     

Flavour mixing of neutrinos and baryon asymmetry of the universe

We investigate baryogenesis in the ν  MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when θ₁₃=0${\theta }_{13}=0$ and θ₂₃=π/4${\theta }_{23}=\pi /4$, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU.     

Admixture of quasi-Dirac and Majorana neutrinos with tri-bimaximal mixing

We propose a realization of the so-called bimodal/schizophrenic model proposed recently. We assume S₄, the permutation group of four objects as flavor symmetry giving tri-bimaximal lepton mixing at leading order. In these models the second massive neutrino state is assumed quasi-Dirac and the remaining neutrinos are Majorana states. In the case of inverse mass hierarchy, the lower bound on the neutrinoless double beta decay parameter mee is about two times that of the usual lower bound, within the range of sensitivity of the next generation of experiments.     

Sneutrino dark matter in gauged inverse seesaw models for neutrinos

Extending the minimal supersymmetric standard model to explain small neutrino masses via the inverse seesaw mechanism can lead to a new light supersymmetric scalar partner which can play the role of inelastic dark matter (IDM). It is a linear combination of the superpartners of the neutral fermions in the theory (the light left-handed neutrino and two heavy standard model singlet neutrinos) which can be very light with mass in ~5-20 GeV range, as suggested by some current direct detection experiments. The IDM in this class of models has keV-scale mass splitting, which is intimately connected to the small Majorana masses of neutrinos. We predict the differential scattering rate and annual modulation of the IDM signal which can be testable at future germanium- and xenon-based detectors.     

Comments on the derivation of the mixing angles

It is pointed out that Fritzsch's derivation of the mixing angles for a six-quark theory based on a SU(2)_L × SU(2)_R × U(1) model is in error. The correct formula for the mixing angles differs significantly from Fritzsch's results.