Vacuum oscillations of solar neutrinos: correlation between spectrum distortion and seasonal variations

Long length vacuum oscillations solution of the solar neutrino problem is discussed. We show that there is a strict correlation between a distortion of the neutrino energy spectrum and an amplitude of seasonal variations of the neutrino flux. The slope parameter which characterizes a distortion of the recoil electron energy spectrum in the Super-Kamiokande experiment and the seasonal asymmetry of the signal have been calculated in a wide range of oscillation parameters. The correlation of the slope and asymmetry gives crucial criteria for identification or exclusion of this solution. For the positive slope indicated by preliminary Super-Kamiokande data we predict (40 - 60) % enhancement of the seasonal variations.Comment: 11 pages, 4 eps figures, LaTeX, analytical study and some explanations added, updated experimental results use

Pontecorvo's Original Oscillations Revisited

We show that a left-handed neutrino $\nu_L$ can oscillate into its $CP$- conjugated state $\bar{\nu}_R$ with maximal amplitude, in direct analogy with $K^0-\bar{K}^0$ oscillations. Peculiarities of such oscillations under different conditions are studied.Comment: LaTeX, 14 pages, 1 figure (not included but available upon request by fax or ordinary mail), SISSA 9/93/EP, IC/93/1

Parametric Resonance in Oscillations of Atmospheric Neutrinos?

We consider a solution of the atmospheric neutrino problem based on oscillations of muon neutrinos to sterile neutrinos: $\nu_{\mu}$ $\leftrightarrow$ $\nu_s$. The zenith angle ($\Theta$) dependences of the neutrino and upward-going muon fluxes in presence of these oscillations are studied. The dependences have characteristic form with two dips: at $\cos \Theta = -0.6 \div -0.2$ and $\cos \Theta = -1.0 \div -0.8$. The latter dip is due to parametric resonance in oscillations of neutrinos which cross the core of the earth. A comparison of predictions with data from the MACRO, Baksan and Super-Kamiokande experiments is given.Comment: 14 pages + 9 eps figures in 6 pages, Latex fil

Rescuing Grand Unification Scenario for Neutrino Mass

The see-saw mechanism for neutrino masses based on the Grand Unification leads to the mass of the heaviest neutrino ($\approx \nu_{\tau}$) in the range $(2 - 3)\cdot 10^{-3}$ eV and hence to a solution of the solar neutrino problem through the \nu_e-\nu_\t conversion. We suggest the existence of a light singlet fermion $S$ which mixes predominantly with muon neutrino through the mixing mass $m_{\mu s} \sim O(1)$ eV. The introduction of such a singlet allows one (i) to solve the atmospheric neutrino problem via the $\nu_{\mu} \leftrightarrow S$ oscillations, (ii) to explain the LSND result and (iii) to get two component hot dark matter in the Universe. The phenomenology of this scenario is considered and the origin of the singlet as well as of the scale m_{\m s} is discussed.Comment: LaTex, 16 pages including one figur

Neutrino mass spectrum and lepton mixing

The program of reconstruction of the neutrino mass and flavor spectrum is outlined and the present status of research is summarized. We describe the role of future solar and atmospheric neutrino experiments, detection of the Galactic supernovae and double beta decay searches in accomplishing this program. The LSND result and four neutrino mass spectra are considered in connection with recent searches for the sterile components in the solar and atmospheric neutrino fluxes.Comment: 8 pages, latex, 4 figures. Talk given at the XIX International Conference on Neutrino Physics and Astrophysics, Neutrino-2000, Sudbury, Canada, 16 - 21 June 200

Towards the Solution of the Solar Neutrino Problem

We discuss various aspects of the solar neutrino spectrum distortion and time variations of fluxes. (i) Oscillations of neutrinos which cross the mantle and the core of the Earth can be parametrically enhanced. The parametric effect gives correct physical interpretation of the calculated day-night asymmetry. (ii) Solution of the $\nu_{\odot}$-problem in schemes with three and more neutrinos which accommodate explanations of other neutrino anomalies, in particular, the atmospheric neutrino anomaly, can lead to complicated distortion of the boron neutrino spectrum. (iii) The study of correlations between time (seasonal or day-night) variations and spectrum distortion will help to identify the solution of the $\nu_{\odot}$-problem.Comment: 10 pages, LaTeX, 9 figures. Invited talk presented at the Neutrino-98 conference, Takayama, Japan, June 1998. Several typos and eps file of fig.5 corrected; reference adde

On the Effective Mass of the Electron Neutrino in Beta Decay

In the presence of mixing between massive neutrino states, the distortion of the electron spectrum in beta decay is, in general, a function of several masses and mixing angles. For $3\nu$-schemes which describe the solar and atmospheric neutrino data, this distortion can be described by a single effective mass, under certain conditions. In the literature, two different definitions for the effective mass have been suggested. We show that for quasi-degenerate mass schemes (with an overall mass scale $m$ and splitting $\Delta m^2$) the two definitions coincide up to $(\Delta m^2)^2/m^4$ corrections. We consider the impact of different effective masses on the integral energy spectrum. We show that the spectrum with a single mass can be used also to fit the data in the case of $4\nu$-schemes motivated, in particular, by the LSND results. In this case the accuracy of the mass determination turns out to be better than $(10 - 15)$.Comment: 15 pages, Version to appear in Phys. Lett.

Neutrinos with Mixing in Twisting Magnetic Fields

Transitions in a system of neutrinos with vacuum mixing and magnetic moments, propagating in matter and transverse magnetic field, are considered. It is shown that in the realistic case of magnetic field direction varying along the neutrino path qualitatively new phenomena become possible: permutation of neutrino conversion resonances, appearance of resonances in the neutrino-antineutrino ($\nu_{lL}\leftrightarrow\bar{\nu}_{lR}$) transition channels, neutrino-antineutrino resonant conversion, large amplitude $\nu_{lL}\leftrightarrow\bar{\nu}_{lR}$ oscillations, merging of different resonances (triple resonances). Possible phenomenological implications of these effects are briefly discussed.Comment: LaTeX, 35 pages, 4 figures (not included but available upon request). In memoriam of Ya.A. Smorodinsky. SISSA-170/92/E

Electron Spin Relaxation in a Semiconductor Quantum Well

A fully microscopic theory of electron spin relaxation by the D'yakonov-Perel' type spin-orbit coupling is developed for a semiconductor quantum well with a magnetic field applied in the growth direction of the well. We derive the Bloch equations for an electron spin in the well and define microscopic expressions for the spin relaxation times. The dependencies of the electron spin relaxation rate on the lowest quantum well subband energy, magnetic field and temperature are analyzed.Comment: Revised version as will appear in Physical Review

Neutrino masses and mixing: Singular mass matrices and Quark-lepton symmetry

We suggest an approach to explain the observed pattern of the neutrino masses and mixing which employs the weakly broken quark-lepton symmetry and does not require introduction of an ad hoc symmetry of the neutrino sector. The mass matrices are nearly equal for all quarks and leptons. They have very small determinants and hierarchical form with expansion parameter lambda = 0.26. The latter can be realized, e.g., in the model with U(1) family symmetry. The symmetry is broken at the lambda^2 level. Large lepton mixing appears as a result of summation of the neutrino and charged lepton rotations which diagonalize the mass matrices in contrast with quark sector where the up quarks and down quarks rotations cancel each other. We show that the flip of the sign of rotation in the lepton sector is a result of the seesaw mechanism which also enhances the neutrino mixing. In this approach one expects, in general, deviation of the 2-3 mixing from maximal, s_{13} \sim (1-3) lambda^2, hierarchical neutrino mass spectrum, and m_{ee} < 10^{-2} eV. The scenario is consistent with the thermal leptogenesis and (in SUSY context) bounds on lepton number violating processes, like mu to e gamma.Comment: 25 pages, one figure, ReVTeX4, Nucl. Phys. B versio