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Register a new userVacuum oscillations and the distorted solar neutrino spectrum observed by Superkamiokande
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The excess of solar-neutrino events above 13 MeV that has been recently observed by Superkamiokande can be explained by vacuum oscillations (VO). If the boron neutrino flux is 20% smaller than the standard solar model (SSM) prediction and the chlorine signal is assumed 30% (or 3.5 sigmas) higher than the measured one, there exists a VO solution that reproduces both the observed boron neutrino spectrum, including the high energy distortion, and the other measured neutrino rates. This solution might already be testable by the predicted anomalous seasonal variation of the gallium signal. Its most distinct signature, a large anomalous seasonal variation of Be7 neutrino flux, can be easily observed by the future detectors, BOREXINO and LENS.
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We find that magnetic neutrino-electron scattering is unaffected by oscillations for vacuum mixing of Dirac neutrinos with only diagonal moments and for Majorana neutrinos with two flavors. For MSW mixing, these cases again obtain, though the effective moments can depend on the neutrino energy. Thus, e.g., the magnetic moments measured with $bar{ u}_e$ from a reactor and $ u_e$ from the Sun could be different. With minimal assumptions, we find a new limit on $mu_{ u}$ using the 825-days SuperKamiokande solar neutrino data: $|mu_{ u}| le 1.5times 10^{-10} mu_B$ at 90% CL, comparable to the existing reactor limit.
Atmospheric neutrinos at low energies, $E lsim 500$ MeV, is known to be a rich source of information of lepton mixing parameters. We formulate a simple perturbative framework to elucidate the characteristic features of neutrino oscillation at around the solar-scale enhancement due to the matter effect. The clearest message we could extract from our perturbation theory is that CP violation in the appearance oscillation probability is large, a factor of $sim 10$ times larger than CP violation at around the atmospheric-scale oscillation maximum. Underlying mechanism for it is that one of the suppression factors on the CP phase dependent terms due to smallness of $Delta m^2_{21} / Delta m^2_{31}$ are dynamically lifted by the solar-scale enhancement. Our framework has a unique feature as a perturbation theory in which large $Delta m^2_{31}$ term outside the key 1-2 sector for the solar-scale resonance does not yield sizeable corrections. On the contrary, the larger the $Delta m^2_{31}$, the smaller the higher order corrections.
We are going back to the roots of the original solar neutrino problem: analysis of data from solar neutrino experiments. The application of standard deviation analysis (SDA) and diffusion entropy analysis (DEA) to the SuperKamiokande I and II data reveals that they represent a non-Gaussian signal. The Hurst exponent is different from the scaling exponent of the probability density function and both Hurst exponent and scaling exponent of the probability density function of the SuperKamiokande data deviate considerably from the value of 0.5 which indicates that the statistics of the underlying phenomenon is anomalous. To develop a road to the possible interpretation of this finding we utilize Mathais pathway model and consider fractional reaction and fractional diffusion as possible explanations of the non-Gaussian content of the SuperKamiokande data.
We propose to exploit the angular distribution of the positrons emitted in the inverse beta decay to extract a possible antineutrino signal from the Superkamiokande background. From the statistics collected in just 101.9 days one obtains a model independent upper bound on the antineutrino flux (for energy greater than 8.3 MeV) Phi < 9*10^4 cm^-2 s^-1 at the 95% C.L. By assuming the same energy spectrum as for the 8B neutrinos, the 95% C.L. bound is Phi < 6*10^4 cm^-2 s^-1. Within three years of data taking, the sensitivity to neutrino-antineutrino transition probability will reach the 1% level, thus providing a stringent test of hybrid oscillation models.
Expressions for neutrino oscillations contain a high degree of symmetry, but typical forms for the oscillation probabilities mask these symmetries. We elucidate the $2^7=128$ symmetries of the vacuum parameters and draw connections to the choice of definitions of the parameters as well as interesting degeneracies. We also show that in the presence of matter an additional set of $2^7=128$ symmetries exist of the matter parameters for a total of $2^{14}=16,384$ symmetries of the vacuum and/or matter parameters in the oscillation probabilities in matter. Due to the complexity of the exact expressions for neutrino oscillations in matter, we show that under certain assumptions, approximate expressions have at most $2^6=64$ additional symmetries of the matter parameters for a total of $2^{13}=8,192$ symmetries. We investigate which of these symmetries apply to numerous approximate expressions in the literature and show that a more careful consideration of symmetries improves the precision of approximations.
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