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C. Giunti

Publications and source records attributed to C. Giunti.

177 records · Page 10Linked to original sources
arXiv1995

ARE THERE STERILE NEUTRINOS IN THE FLUX OF SOLAR NEUTRINOS ON THE EARTH?

It is shown that the future SNO and Super-Kamiokande experiments, in which high energy $^8\mathrm{B}$ neutrinos will be detected through the observation of CC, NC and $ν$--$e$ elastic scattering processes, could allow to reveal in a model independent way the presence of sterile neutrinos in the flux of solar neutrinos on the earth. Lower bounds for different averaged values of the probability of transition of solar $ν_e$'s into sterile states and for the total flux of $^8\mathrm{B}$ neutrinos are derived in terms of measurable quantities. The possibilities to reveal the presence of $ν_μ$ and/or $ν_τ$ in the solar neutrino flux on the earth are also considered and the case of transitions of solar $ν_e$'s only into sterile states is discussed. Some numerical results for a simple model with $ν_e$--$ν_s$ mixing are given.

hep-ph↗
arXiv1995

Atmospheric Neutrino Problem in Maximally-Mixed Three Generations of Neutrinos

Motivated by the indication that both the atmospheric and the solar neutrino puzzles may simultaneously be solved by (vacuum as well as matter-induced resonant) oscillations of two generations of neutrinos with large mixing, we have analyzed the data on the atmospheric and solar neutrinos assuming that all {\it three} neutrinos are maximally mixed. It is shown that the values of $ Δm^2 $ obtained from the two-generation analyses are still valid even in the three-generation scheme, i.e. the two puzzles can be solved simultaneously if $ Δm_{31}^2 \simeq 10^{-2} \, \mathrm{eV}^2 $ for the atmospheric neutrinos and $ Δm_{21}^2 \simeq 10^{-10} \, \mathrm{eV}^2 $ for solar neutrinos in the maximally mixed three-generation scheme.

hep-ph↗
arXiv1995

A MODEL INDEPENDENT APPROACH TO FUTURE SOLAR NEUTRINO EXPERIMENTS

It is shown that from the data of future solar neutrino experiments (SNO and Super-Kamiokande), in which high-energy $^8\mathrm{B}$ neutrinos will be detected, it will be possible in a model independent way: 1) To reveal the presence of sterile neutrinos in the flux of solar neutrinos on the earth; 2) To obtain the initial flux of $^8\mathrm{B}$ $ν_e$'s; 3) To determine the probability of $ν_e$'s to survive as a function of neutrino energy.

hep-ph↗
arXiv1994

A Model Independent Analysis of Solar Neutrino Data

We present the results of a solar model independent analysis of the existing solar neutrino data in the case of $ν_{e}\toν_{μ(τ)}$ MSW transitions. We considered two cases. In the first case no assumptions on the values of the total fluxes of neutrinos from all reactions have been made. In the second case we constrained the values of the neutrino fluxes within some wide limits that take into account the predictions of the existing Standard Solar Models. We show that in both cases the existing data allow to exclude rather large regions in the plane of the parameters $ Δm^2 $ and $ \sin^2 2θ$.

hep-ph↗
arXiv1994

A Model Independent Analysis of Solar Neutrino Data

The results of a solar model independent analysis of the existing solar neutrino data under the assumption of MSW transitions in matter or vacuum oscillations (in the cases of $ν_{e}$--$ν_μ(ν_τ)$ and $ν_{e}$--$ν_{\mathrm{S}}$ mixing) are presented. The analysis was done in two cases. In the first case no assumptions on the value of the total fluxes of neutrinos from all reactions has been made. In the second case some boundaries for the values of the neutrino fluxes, that take into account the predictions of different standard solar models, are imposed. It is shown that rather large regions of the parameters $ Δm^2 $ and $ \sin^2 2θ$ are excluded by the existing data. It is also shown that the astrophysical solution of the solar neutrino problem can be excluded only in the case in which limitations on the values of the solar neutrino fluxes are imposed.

hep-ph↗
arXiv1994

A Model Independent Approach to Future Solar Neutrino Experiments

We discuss here what model independent information about properties of neutrinos and of the sun can be obtained from future solar neutrino experiments (SNO, Super-Kamiokande). It is shown that in the general case of transitions of solar $ν_e$'s into $ν_μ$ and/or $ν_τ$ the initial $^8\mathrm{B}$ neutrino flux can be measured by the observation of NC events. From the CC measurements the $ν_e$ survival probability can be determined as a function of neutrino energy. The general case of transitions of solar $ν_e$'s into active as well as sterile neutrinos is considered. A number of relations between measurable quantities the test of which will allow to answer the question whether there are sterile neutrinos in the solar neutrino flux on the earth are derived. Transitions of solar $ν_e$'s into active and sterile states due to neutrino mixing and Dirac magnetic moments or into active left-handed neutrinos and active right-handed antineutrinos due to neutrino mixing and Majorana transition magnetic moments are also considered. It is shown that future solar neutrino experiments will allow to distinguish between the cases of Dirac and Majorana magnetic moments.

hep-ph↗
arXiv1993

Future Solar Neutrino Experiments and Neutrino Spin-Flavour Precession

The main features of the observables in the SNO and Super-Kamiokande solar neutrino experiments in the case of neutrino spin and/or spin-flavour precession in the magnetic field of the sun are discussed. It is shown without any model dependent assumption that in the case of Majorana transition magnetic moments the NC event rate $N^{\mathrm{NC}}$ does not depend on time and a measurement of $N^{\mathrm{NC}}$ will allow to determine the initial flux of $^8\mathrm{B}$ neutrinos with a theoretical uncertainty of a few \%. In the case of Dirac magnetic moments the NC event rate will depend on time and we obtain a model independent lower bound for the transition probability of initial $ν_e$'s into right-handed sterile neutrinos.

hep-ph↗
arXiv1993

Neutrino Mixing and Future Solar Neutrino Experiments

Possibilities of a model independent treatment of the data from future real-time solar neutrino experiments (SNO, Super-Kamiokande and others) are discussed. It is shown that in the general case of transitions of the initial solar $ν_e$'s into $ν_μ$ and/or $ν_τ$ the total flux of initial 8B neutrinos and the $ν_e$ survival probability can be determined directly from the experimental data. Lower bounds for the probability of transition of solar $ν_e$'s into all possible sterile states are derived and expressed through measurable quantities.

hep-ph↗
arXiv1993

Sterile Neutrinos and Future Solar Neutrino Experiments

It is shown that future solar neutrino experiments (SNO, Super-Kamiokande and others), in which high energy neutrinos will be detected (mostly from 8B decay), may allow to answer in a model independent way the question whether there are transitions of solar $ν_e$'s into sterile states. No assumptions about the initial flux of 8B neutrinos are done. Lower bounds for the probability of transition of solar $ν_e$'s into all possible sterile states are derived and expressed through measurable quantities.

hep-ph↗
arXiv1993

On the Proton Form Factors in the Time-Like Region

The process $ \bar{p} p \rightarrow e^{-} e^{+} $ is considered in the general case of polarized initial particles. A relation between the difference of the phases of the electromagnetic form factors $G_M$ and $G_E$ in the time-like region and measurable asymmetries is derived. It is shown that the moduli of the form factors can be determined from measurements of the total unpolarized cross section and of the integral asymmetry for longitudinally polarized (or transversely polarized) $\bar{p}$ and $p$. The behaviour of the proton form factors at high $q^2$ in the time-like region is also discussed. From the Phragmén-Lindelöf's theorem it follows that the asymptotical behaviour of the form factors in the space-like and time-like regions must be the same. An analysis of experimental data in both regions based on perturbative QCD is presented.

hep-ph↗
arXiv1993

On the Treatment of Neutrino Oscillations Without Resort to Weak Eigenstates

We discuss neutrino oscillations in the framework of the quantum field theory without introducing the concept of neutrino weak eigenstates. The external particles are described by wave packets and the different mass eigenstate neutrinos propagate between the production and detection interactions, which are macroscopically localized in space-time. The time-averaged cross section, which is the measurable quantity in the usual experimental setting, is calculated. It is shown that only in the extremely relativistic limit the usual quantum mechanical oscillation probability can be factored out of the cross section.

hep-ph↗
arXiv1993

Towards a Model Independent Treatment of Future Solar Neutrino Data

Possibilities of a model independent treatment of the data from future real-time solar neutrino experiments (SNO, Super-Kamiokande and others) are discussed. It is shown that in the general case of transitions of the initial solar $ν_e$'s into $ν_μ$ and/or $ν_τ$ the total flux of initial $^8\mathrm{B}$ neutrinos and the $ν_e$ survival probability can be determined directly from the experimental data. Relations between observable quantities are derived, which, if confronted with the experimental data, would allow to reveal the presence of sterile neutrinos in the solar neutrino flux on the earth. Neutrino transitions due to spin and resonant spin-flavour precession in the magnetic field of the sun are shortly discussed.

hep-ph↗
arXiv1992

See-Saw Type Mixing and $ ν_μ \to ν_τ $ Oscillations

We consider $ ν_μ \to ν_τ $ oscillations under the assumption that there is a see-saw type mixing of the light neutrinos with heavy Majorana particles. It is shown that the existing data, including the recent LEP data, do not exclude the possibility that the additional terms in the transition probability due to this mixing could be of the same order of magnitude as the usual oscillating term. Detail investigations of $ ν_μ \to ν_τ $ transitions in future CERN and Fermilab experiments could allow to get informations not only about the neutrino masses and mixing but also about the mixing of neutrinos with heavy Majorana particles.

hep-ph↗
arXiv1992

Oscillations of Pseudo-Dirac Neutrinos and the Solar Neutrino Problem

The oscillations of pseudo-Dirac neutrinos in matter are discussed and applied to the solar neutrino problem. Several scenarios such as both $ν_e$ and $ν_μ$ being pseudo-Dirac and only $ν_e$ or $ν_μ$ being pseudo-Dirac are examined. It is shown that the allowed region in the mass-mixing angle parameter space obtained by comparing the solar neutrino data with the calculations based on the standard solar model and the MSW effect is not unique. The results depend on the nature of neutrinos; for example, if both $ν_e$ and $ν_μ$ are pseudo-Dirac, the allowed region determined by the current solar neutrino data does not overlap with that obtained in the usual case of pure Dirac or Majorana neutrinos.

hep-ph↗