Solar neutrino oscillations from superstrings

A recently proposed model of neutrino mass based on the heterotic superstring is shown to lead naturally to large oscillations of the SU(2)-doublet neutrino into sterile fermions leading to the possibility of substantial depletion of the solar electron neutrino flux as suggested by Davis' results. The model also leads to a psuedo-Dirac nuetrino with m_v = 10–20 eV, without conflict with null searches for neutrinoless double beta decay.     

Solar neutrino oscillations in the quasi-vacuum regime

Motivated by recent experimental data, we study solar neutrino oscillations in the range δm²/E ε [10⁻¹⁰, 10⁻⁷] eV²/MeV. In this range vacuum oscillations become increasingly affected by (solar and terrestrial) matter effects for increasing δm², smoothly reaching the MSW regime. A numerical study of matter effects in such “quasi-vacuum” regime is performed. The results are applied to the analysis of the recent solar neutrino phenomenology.     

Phenomenology of neutrino oscillations

The phenomenology of solar, atmospheric, supernova and laboratory neutrino oscillations is described. Analytical formulae for matter effects are reviewed. The results from oscillations are confronted with neutrinoless double beta decay.     

Search for neutrino oscillations

A search for ν_μ→ν_e and oscillations has been conducted with the AGS wide-band neutrino beam at the Brookhaven National Laboratory. We find more ν_e ( _e) interactions than were expected on the basis of the number of incident ν_e ( _e) calculated as part of the neutrino beam. The excess is about a factor two over the expectation, the statistical significance being about two and a half standard deviations for ν_e and weaker for _e.     

Paradoxes of neutrino oscillations

Despite the theory of neutrino oscillations being rather old, some of its basic issues are still being debated in the literature. We discuss a number of such issues, including the relevance of the “same energy” and “same momentum” assumptions, the role of quantum-mechanical uncertainty relations in neutrino oscillations, the dependence of the coherence and localization conditions that ensure the observability of neutrino oscillations on neutrino energy and momentum uncertainties, the question of (in)dependence of the oscillation probabilities on the neutrino production and detection processes, and the applicability limits of the stationary-source approximation. We also develop a novel approach to calculation of the oscillation probability in the wave-packet approach, based on the summation/integration conventions different from the standard one, which allows a new insight into the “same energy” vs. “same momentum” problem. We also discuss a number of apparently paradoxical features of the theory of neutrino oscillations. The text was submitted by the authors in English.     

Solar neutrino spectroscopy

Since the pioneering experiment of R. Davis et al., which started neutrino astronomy by measuring the solar neutrinos via the inverse beta decay reaction on ³⁷Cl, all solar neutrino experiments find a considerably lower flux than expected by standard solar models. This finding is generally called the solar neutrino problem. Many attempts have been made to explain this result by altering the solar models, or assuming different nuclear cross sections for fusion processes assumed to be the energy sources in the sun.There have been performed numerous experiments recently to investigate the different possibilities to explain the solar neutrino problem. These experiments covered solar physics with helioseismology, nuclear cross section measurements, and solar neutrino experiments.Up to now no convincing explanation based on “standard” physics was suggested. However, assuming nonstandard neutrino properties, i.e. neutrino masses and mixing as expected in most extensions of the standard theory of elementary particle physics, natural solutions for the solar neutrino problem can be found.It appears that with this newly invented neutrino astronomy fundamental information on astrophysics as well as elementary particle physics are tested uniquely. In this contribution an attempt is made to review the situation of the neutrino astronomy for solar neutrino spectroscopy and discuss the future prospects in this field.     

Solar neutrino decay

We re-examine the neutrino decay solution to the solar neutrino problem in light of the new data from GALLEX II and Kamiokande III. We compare the experimental data with the solar models of Bahcall and Pinsonneault and Turck-Chieze and find that neutrino decay is ruled out as a solution to the solar neutrino problem at better than the 98% CL even when solar model uncertainties are taken into account.     

Supernova neutrino nucleosynthesis of light elements with neutrino oscillations

Light element synthesis in supernovae through neutrino-nucleus interactions, i.e., the v process, is affected by neutrino oscillations in the supernova environment. There is a resonance of 13-mixing in the O/C layer, which increases the rates of charged-current -process reactions in the outer He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and 1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing resonance, compared to those without neutrino oscillations. In the case of an inverted mass hierarchy and a nonadiabatic 13-mixing resonance, the increase in the 7Li and 11B yields is much smaller. Observations of the 7Li/11B ratio in stars showing signs of supernova enrichment could thus provide a unique test of neutrino oscillations and constrain their parameters and the mass hierarchy.     

Charged lepton and neutrino oscillations

Problems long present in the conventional formalism employed for neutrino oscillations are discussed. We here develop a more satisfactory framework based on the Dirac equation and its propagators. When 4-momentum conservation is strictly enforced, there will be induced oscillations in space (but not between generations) for the charged leptons, e.g. and , produced in association with the neutrinos. The oscillations are computed explicitly for the pion decay . Leptonic decays of the are also briefly discussed. Received: 15 October 1996 / Revised version: 15 June 1997 / Published online: 20 February 1998     

Lepton mixing and neutrino oscillations

The present article is a review of phenomena connected with neutrino oscillations. Mixing of two neutrinos (Majorana as well as Dirac) with masses m₁ and m₂ is considered in detail. It is shown that the hypothesis of lepton mixing is not in contradiction with the existing data if |m₁²?m₂²| ? 1 (eV)². Possible experiments designed to reveal neutrino oscillations at reactor, meson factory and high energy accelerator facilities are considered. In such experiments oscillation might be found if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 0.01}\text{(eV)}{}^2$. The possibilities of searching for oscillations by experiments on cosmic ray neutrinos and especially on solar neutrinos are discussed in detail. The last experiments have an incredible high sensitivity from the point of view of testing the lepton mixing hypothesis (oscillation effects might be observable if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 10}{}^{\mathrm{?12}}\text{(eV)}{}^2$). The “solar neutrino puzzle” is also discussed from the point of view of lepton mixing. Neutrino oscillations are considered then in the case where in nature there exist N ? 2 neutrino types.In conclusion the case of heavy lepton mixing is considered. It is shown that in a concrete scheme with right-handed currents, the probabilities of such processes as μ → eγ, μ → 3e etc. can be close to existing experimental upper limits, provided the heavy lepton masses are of an order of a few GeV, whereas the probabilities of the above processes are entirely negligible if only neutrinos are mixed.