Vacuum solutions of neutrino anomalies through a softly broken U(1) symmetry

We discuss an extended model which naturally leads to mass scales and mixing angles relevant for understanding both the solar and atmospheric neutrino anomalies in terms of the vacuum oscillations of the three known neutrinos. The model uses a softly broken –– symmetry and contains a heavy scale GeV. The –– symmetric neutrino masses solve the atmospheric neutrino anomaly while breaking of –– generates the highly suppressed radiative mass scale needed for the vacuum solution of the solar neutrino problem. All the neutrino masses in the model are inversely related to , thus providing seesaw-type of masses without invoking any heavy right-handed neutrinos. The possible embedding of the model into an SU(5) grand unified theory is discussed. Received: 5 August 1999 / Revised version: 18 November 1999 / Published online: 6 April 2000     

A new three-flavor oscillation solution of the solar neutrino deficit in <Emphasis Type="Italic">R</Emphasis>-parity violating supersymmetry

We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV² in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos nor CP violation in terrestrial neutrino experiments. Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002     

Neutrino mass and oscillation: An introductory review

After a brief introduction to neutrino mass via the see-saw model I discuss neutrino mixing and oscillation, first in vacuum and then its matter enhancement. Then the solar and atmospheric neutrino oscillation data are briefly reviewed. Finally I discuss the problem of reconciling hierarchical neutrino masses with at least one large mixing, as implied by these data. A minimal see-saw model for reconciling the two is discussed.     

Testing the vacuum oscillation and the MSW solutions of the solar neutrino problem

Solar model independent tests of the vacuum oscillation and MSW solutions of the solar neutrino problem are considered. Detailed predictions for time (seasonal) variations of the signals due to neutrino oscillations in vacuum are given for the future solar neutrino detectors (SNO, Super-Kamiokande, BOREXINO, HELLAZ). Results on the distortions of the spectra of ⁸B neutrinos, and of e⁻ from the reaction ν + e⁻ → ν + e⁻ induced by ⁸B neutrinos, are presented in the cases of vacuum oscillations or MSW transitions for a large number of values of the relevant parameters. The possibilities to distinguish between the vacuum oscillation, the MSW adiabatic, and the MSW nonadiabatic transitions in the future solar neutrino experiments are discussed.     

Inertial effects on neutrino oscillations

The inertial effects on neutrino oscillations induced by the acceleration and angular velocity of a reference frame are calculated. Such effects have been analyzed in the framework of the solar and atmospheric neutrino problem. Received: 19 March 1999 / Revised version: 9 July 1999 / Published online: 8 December 1999     

Oscillating neutrinos: theory vs experiment

Possible hints on neutrino masses are reviewed. They come from the deficits in the solar as well as atmospheric neutrinos and from need of a significant amount of hot component in the dark matter of the universe. The role of three generation mixing in simultaneously solving the solar and atmospheric neutrino problem is discussed. All the three hints can be reconciled if three neutrinos are almost degenerate. Models for neutrino masses and mixing implied by the above hints are briefly discussed.     

Analysis of a three flavor neutrino oscillation fit to recent Super-Kamiokande data

We have analyzed the most recent available Super-Kamiokande data in a three flavor neutrino oscillation model. We have here neglected possible matter effects and we performed a fit to atmospheric and solar Super-Kamiokande data. We have investigated a large parameter range where the mixing angles were restricted to , , and the mass squared differences were taken to be in the intervals and , i.e., the hierarchy between the mass squared differences is not completely determined. This yielded a best solution characterized by the parameter values , , , , and , which shows that the analyzed experimental data speak in favor of a bimaximal mixing scenario with one of the mass squared differences in the “just-so” domain and the other one in the range capable of providing a solution to the atmospheric neutrino problem. Received: 4 July 2000 / Published online: 27 October 2000     

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.     

Reconciling cold dark matter with COBE/IRAS plus solar and atmospheric neutrino data

We present a model where an unstable MeV Majorana tau neutrino can naturally reconcile the cold dark matter model (CDM) with cosmological observations of large and small scale density fluctuations and, simultaneously, with data on solar and atmospheric neutrinos. The solar neutrino deficit is explained through long wavelength, so-called just-so oscillations involving conversions of ν_e into both ν_μ and a sterile species ν_s , while atmospheric neutrino data are explained through ν_μ to ν_e conversions. Future long baseline neutrino oscillation experiments, as well as some reactor experiments will test this hypothesis. The model is based on the spontaneous violation of a global lepton number symmetry at the weak scale. This symmetry plays a key role in generating the cosmologically required decay of the ν_τ with lifetime τ_ντ ≈ 10²-10⁴ seconds, as well as the masses and oscillations of the three light neutrinos ν_e, ν_μ and ν_s required in order to account for solar and atmospheric neutrino data. It also leads to the invisibly decaying Higgs signature that can be searched at LEP and future particle colliders.     

Linking solar and long baseline terrestrial neutrino experiments

We show that, in the framework of three light neutrino species with hierarchical masses and assuming no fine tuning between the entries of the neutrino mass matrix, one can use the solar neutrino data to obtain information on the element U(e3) of the lepton mixing matrix. Conversely, a measurement of U(e3) in atmospheric or long baseline accelerator or reactor neutrino experiments would help discriminate between possible oscillation solutions of the solar neutrino problem.     

Neutrino textures in light of Super-Kamiokande data and a realistic string model

Motivated by the Super-Kamiokande atmospheric neutrino data, we discuss possible textures for Majorana and Dirac neutrino masses within the see-saw framework. There are two main purposes of this paper: first, to gain intuition into this area from a purely phenomenological analysis, and second, to explore to what extent it may be realized in a specific model. We comment initially on the simplified two-generation case, emphasizing that large mixing is not incompatible with a large hierarchy of mass eigenvalues. We also emphasize that renormalization-group effects may amplify neutrino mixing, and we present semi-analytic expressions for estimating this amplification. Several examples are then given of three-family neutrino mass textures, which may also accommodate the persistent solar neutrino deficit, with different assumptions for the neutrino Dirac mass matrices. We comment on a few features of neutrino mass textures arising in models with a U(1) flavour symmetry. Finally, we discuss the possible pattern of neutrino masses in a “realistic” flipped SU(5) model derived from string theory, illustrating how a desirable pattern of mixing may emerge. Both small- or large-angle MSW solutions are possible, while a hierarchy of neutrino masses appears more natural than near-degeneracy. This model contains some unanticipated features that may be relevant in other models also: The neutrino Dirac matrices may not be related closely to the quark mass matrices, and the heavy Majorana states may include extra gauge-singlet fields. Received: 6 November 1998 / Published online: 18 June 1999     

Resonant neutrino oscillations and the neutrino signature of supernovae

We examine the effects of resonant neutrino oscillations, proposed as a solution to the solar neutrino puzzle, on the neutrino signature of a Type II supernova. We find that, for parameters corresponding to an adiabatic conversion of most of the ⁸B neutrino flux, the supernova neutrino signal in a water-Čerenkov detector is altered in the following way: (1) The isotropic-to-directional event ratio increases; (2) The short time scale neutronization burst signal decreases by a factor 7, perhaps rendering it unobservable. Detection of these changes would allow one to distinguish between neutrino oscillations and solar model alterations as solutions to the solar neutrino problem. We also note that mixing of the higher energy ν_μ and ν_r's to ν_e's will enhance detection of the thermally produced ν-flux.     

A gut solution to the solar neutrino problem

Within the supersymmetric flipped SU(5)×U(1) model, we propose a mechanism for realization of the Voloshin-Vysotsky-Okun solution to the solar neutrino problem by attributing a large magnetic moment to the electron neutrino, as required to explain the solar neutrino data.     

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.     

The discovery of neutrino oscillations

The Nobel Prize for physics 2015 was awarded to Takaaki Kajita and Arthur McDonald for the discovery of neutrino oscillations, showing that neutrinos have a mass. This article describes the two areas of research namely the atmospheric neutrino anomaly and the problem of missing solar neutrinos which lead to these groundbreaking discoveries.     

Global analysis of solar and atmospheric neutrino data

A global analysis of solar (including the recent SNO result), atmospheric, and reactor neutrino data is presented in terms of three-and four-neutrino oscillations. We first present the allowed regions of solar and atmospheric oscillation parameters assuming three-neutrino families, showing that in this framework it is possible to reconcile the two anomalies and providing an unified fit of all the observables at a time. Then, we consider scenarios where a sterile neutrino is added to the three standard ones and the mass spectra present two separate doublets. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations, showing that, although the Super-Kamiokande data disfavor both the pure ν_μ→ν _s atmospheric channel and, in combination with SNO, the pure ν _e →ν _s solar channel, the result from the combined analysis still favors close-to-pure active and sterile oscillations and disfavors oscillations into a near-maximal active-sterile admixture.     

中微子质量和中微子振荡实验

本介绍中微子质量测量的历史和现状。介绍太阳中微子丢失实验的结果和大气μ中微子丢失实验结果。这些结果表明存在中微子振荡,即中微子具有质量。它是超出标准模型的信号。本还介绍了21世纪初研究中微子振荡的若干重要实验,例如长基线中微子振荡实验以及建造μ子 贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Neutrino Oscillations in Caianiello's Quantum Geometry Model

Neutrino flavor oscillations are analyzed in the framework of Quantum Geometry model proposed by Caianiello. In particular, we analyze the consequences of the model for accelerated neutrino particles that experience an effective Schwarzschild geometry modified by the existence of an upper limit on the acceleration, which implies a violation of the equivalence principle. We find a shift of quantum-mechanical phase of neutrino oscillations, which depends on the energy of neutrinos as E³. Implications on atmospheric and solar neutrinos are discussed.