Confronting mass-varying neutrinos with MiniBooNE

We study the proposal that mass-varying neutrinos could provide an explanation for the LSND signal for \bar\nu_mu to \bar\nu_e oscillations. We first point out that all positive oscillation signals occur in matter and that three active mass-varying neutrinos are insufficient to describe all existing neutrino data including LSND. We then examine the possibility that a model with four mass-varying neutrinos (three active and one sterile) can explain the LSND effect and remain consistent with all other neutrino data. We find that such models with a 3+1 mass structure in the neutrino sector may explain the LSND data and a null MiniBooNE result for 0.10 < \sin^2 2\theta_x < 0.30. Predictions of the model include a null result at Double-CHOOZ, but positive signals for underground reactor experiments and for \nu_\mu to \nu_e oscillations in long-baseline experiments.Comment: 22 pages, 3 figures, 1 table. Comment added about recent MINOS dat

On mixing angles and magnetic moment of heavy tau neutrino

If the magnetic moment of unstable tau neutrinos with the mass of $O$(MeV) is in the region of $10^{-8}\mu_{B} \lesssim \mu_{\nu_{\tau}} \lesssim 10^{-6}\mu_{B}$, it is compatible with the present experimental and cosmological bounds. It is pointed out here, that if the tau neutrino has such a large magnetic moment and can oscillate into a neutrino of another flavour the results from $\nu e$ scattering experiment at LAMPF constrain the tau neutrino mixing angles to $sin^{2}2\theta_{e \tau} \lesssim 2\times 10^{-6} - 2\times 10^{-2}$ and $sin^{2}2\theta_{\mu\tau} \lesssim 10^{-6} - 10^{-2}$ depending on the magnetic moment value in the allowed region.Comment: 5 pages, LaTe

Does the neutrino magnetic moment have an impact on solar neutrino physics?

Solar neutrino observations coupled with the recent KamLAND data suggest that spin-flavor precession scenario does not play a major role in neutrino propagation in the solar matter. We provide approximate analytical formulas and numerical results to estimate the contribution of the spin-flavor precession, if any, to the electron neutrino survival probability when the magnetic moment and magnetic field combination is small.Comment: 7 pages, 1 figure

Global neutrino data and recent reactor fluxes: status of three-flavour oscillation parameters

We present the results of a global neutrino oscillation data analysis within the three-flavour framework. We include latest results from the MINOS long-baseline experiment (including electron neutrino appearance as well as anti-neutrino data), updating all relevant solar (SK II+III), atmospheric (SK I+II+III) and reactor (KamLAND) data. Furthermore, we include a recent re-calculation of the anti-neutrino fluxes emitted from nuclear reactors. These results have important consequences for the analysis of reactor experiments and in particular for the status of the mixing angle $\theta_{13}$. In our recommended default analysis we find from the global fit that the hint for non-zero $\theta_{13}$ remains weak, at 1.8$\sigma$ for both neutrino mass hierarchy schemes. However, we discuss in detail the dependence of these results on assumptions concerning the reactor neutrino analysis.Comment: 15 pages, 10 figures and 2 tables, v2: corrected version, main conclusions unchanged, references adde

Sensitivities of Low Energy Reactor Neutrino Experiments

The low energy part of the reactor neutrino spectra has not been experimentally measured. Its uncertainties limit the sensitivities in certain reactor neutrino experiments. The origin of these uncertainties are discussed, and the effects on measurements of neutrino interactions with electrons and nuclei are studied. Comparisons are made with existing results. In particular, the discrepancies between previous measurements with Standard Model expectations can be explained by an under-estimation of the low energy reactor neutrino spectra. To optimize the experimental sensitivities, measurements for \nuebar-e cross-sections should focus on events with large ($>$1.5 MeV) recoil energy while those for neutrino magnetic moment searches should be based on events $<$100 keV. The merits and attainable accuracies for neutrino-electron scattering experiments using artificial neutrino sources are discussed.Comment: 25 pages, 9 figure

Production and Decay of the Ge73-m Metastable State in a Low-Background Germanium Detector

The $\ge73m$ metastable states decay with a very characteristic signature which allow them to be tagged event-by-event. Studies were performed using data taken with a high-purity germanium detector in a low-background laboratory near a nuclear power reactor core where \nuebar-flux was $\rm{6.4 \times 10^{12} ~ cm^{-2} s^{-1}}$. The measured average and equilibrium production rates of $\ge73m$ were $\rm{(8.7 \pm 0.4)}$ and $\rm{(6.7 \pm 0.3) ~ kg^{-1} day^{-1}}$, respectively. The production channels were studied and identified. By studying the difference in the production of $\ge73m$ between the reactor ON and OFF spectra, the limiting sensitivities at the range of $\rm{\sim 10^{-42} - 10^{-43} ~ cm^2}$ for the cross-sections of neutrino-induced nuclear transitions were derived. The dominant background are due to $\beta$-decays of cosmic-ray induced $^{73}$Ga. The prospects of enhancing the sensitivities at underground locations are discussed.Comment: 16 pages, 10 figure

Pontecorvo neutrino-antineutrino oscillations: theory and experimental limits

We study Pontecorvo neutrino-antineutrino oscillations both in vacuum and in matter within a field theoretic approach, showing that this phenomenon can occur only if neutrinos have a Dirac-Majorana mass term. We find that matter effects suppress these oscillations and cannot explain the solar neutrino problem. On the contrary, a vacuum neutrino-antineutrino oscillations solution to this problem exists. We analyze this solution and available data from laboratory experiments giving stringent limits on $\nu_e$ and $\nu_{\mu}$ Majorana masses.Comment: 11 pages, Latex2

Three flavor neutrino oscillation analysis of the Superkamiokande atmospheric neutrino data

Superkamiokande atmospheric neutrino data for 535 days are analyzed in the framework of three flavor oscillations with mass hierarchy. It is shown that the best fit point is very close to the pure maximal $\nu_\mu\leftrightarrow\nu_\tau$ case and $\Delta m^2 \simeq 7\times10^{-3}$ eV$^2$. The allowed region at 90 %CL is given and the implications to the long baseline experiments are briefly discussed.Comment: 8 pages + 1 Table + 28 PostScript figures updated using 535 day dat

Constraints on Three-Neutrino Mixing from Atmospheric and Reactor Data

Observations of atmospheric neutrinos are usually analyzed using the simplifying approximation that either $\nu_\mu \leftrightarrow \nu_\tau$ or $\nu_e \leftrightarrow \nu_\mu$ two-flavor mixing is relevant. Here we instead consider the data using the simplifying approximation that only one neutrino mass scale is relevant. This approximation is the minimal three-flavor notation that includes the two relevant two-flavor approximations. The constraints in the parameter space orthogonal to the usual, two-flavor analyses are studied.Comment: 15 pages, preprint IUHET-26

Spin-Flavour Oscillations and Neutrinos from SN1987A

The neutrino signal from SN1987A is analysed with respect to spin-flavour oscillations between electron antineutrinos, $\bar{\nu}_{e}$, and muon neutrinos, $\nu_{\mu}$, by means of a maximum likelihood analysis. Following Jegerlehner et al. best fit values for the total energy released in neutrinos, $E_t$, and the temperature of the electron antineutrino, $T_{\bar{\nu}_{e}}$, for a range of mixing parameters and progenitor models are calculated. In particular the dependence of the inferred quantities on the metallicity of the supernova is investigated and the uncertainties involved in using the neutrino signal to determine the neutrino magnetic moment are pointed out.Comment: 14 pages, RevTeX, 4 figures, to appear in Physical Review