Observable Medium Effects For Atmospheric Neutrinos

We discuss the possibility to observe matter effects in atmospheric neutrino oscillations. The main conclusion is that an impact on the nu_mu survival probability requires the action of the MSW resonance, which becomes visible for baselines above ~7000 km. The associated muon charge asymmetry carries information on theta_{13} and the sign of Dm^2_{31}.Comment: 7 pp, 2 fig. Talk given at the EPS-Conference on HEPP, Budapest (Hungary), July 2001, to be published in the Proceeding

The sign of dm2_{31} and the muon-charge asymmetry for atmospheric neutrinos

We discuss the possibility to measure the sign of dm2_{31} from matter-induced charge asymmetries in atmospheric neutrino oscillations. The main conclusion is that an impact on the nu_mu survival probability requires the action of the MSW resonance, which becomes visible for baselines above \~7000 km.Comment: 6 pp, 1 fig. Talk given at the 7th International Workshop on Topics in Astroparticles and Underground Physics (TAUP2001), Laboratori Nazionali del Gran Sasso, Italy, September 8-12, 200

Sterile neutrino decay and the LSND experiment

We propose a new explanation of the intriguing LSND evidence for electron antineutrino appearance in terms of heavy (mostly sterile) neutrino decay via a coupling with a light scalar and light (mostly active) neutrinos. We perform a fit to the LSND data, as well as all relevant null-result experiments, taking into account the distortion of the spectrum due to decay. By requiring a coupling g ~ 10^{-5}, a heavy neutrino mass m_4 ~ 100 keV and a mixing with muon neutrinos |U_{mu 4}|^2 ~ 10^{-2}, we show that this model explains all existing data evading constraints that disfavor standard (3+1) neutrino models.Comment: 3pp. Talk given at 9th International Conference on Astroparticle and Underground Physics (TAUP 2005), Zaragoza, Spain, 10-14 Sep 200

The Earth Mantle-Core Effect in Matter-Induced Asymmetries for Atmospheric Neutrino Oscillations

Earth medium effects in the three-neutrino oscillations of atmospheric neutrinos are observable under appropriate conditions. This paper generalizes the study of the medium effects and the possibility of their observation in the atmospheric neutrino oscillations from the case of neutrinos traversing only the Earth mantle, where the density is essentially constant, to the case of atmospheric neutrinos crossing also the Earth core. In the latter case new resonance-like effects become apparent. We calculate the CPT-odd asymmetry for the survival probability of muon neutrinos and the observable muon-charge asymmetry, taking into account the different atmospheric neutrino fluxes, and show the dependence of these asymmetries on the sign of $\Delta m^{2}_{3 1}$ and on the magnitude of the mixing angle $\theta_{13}$. A magnetized detector with a sufficiently good neutrino momentum resolution is required for the observation of the muon-charge asymmetry generated by the Earth mantle-core effect.Comment: 14 pages, 5 figure

Are small neutrino masses unveiling the missing mass problem of the Universe?

We present a scenario in which a remarkably simple relation linking dark matter properties and neutrino masses naturally emerges. This framework points towards a low energy theory where the neutrino mass originates from the existence of a light scalar dark matter particle in the MeV mass range. A very surprising aspect of this scenario is that the required MeV dark matter is one of the favoured candidates to explain the mysterious emission of 511 keV photons in the centre of our galaxy. A possible interpretation of these findings is that dark matter is the stepping stone of a theory beyond the standard model instead of being an embarrassing relic whose energy density must be accounted for in any successful model building.Comment: 4pages, 2 figures. Two paragraphs have been added. One for the complex case; the other one for the UV completio

On the Atmospheric Neutrino Oscillations, theta13 and Neutrino Mass Hierarchy

We give predictions for the up-down asymmetry in the Nadir angle dependence of the ratio Nmu/Ne of the rates of the mu-like and e-like multi-GeV events measured in water-Cerenkov detectors (Super-Kamiokande, etc.) in the case of 3-neutrino oscillations of the atmospheric nu_e (antinu_e) and nu_mu (antinu_mu), driven by one neutrino mass squared difference, |Delta m^2_{atm}| = |Delta m^2_{31}| ~ (2.0 - 3.0) 10^{-3} eV^2 >> Delta m^2_{21} = Delta m^2_{sol}. This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin^2(theta13) and sin^2(theta23), theta13 and theta23 being the neutrino mixing angle limited by the CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric nu_mu -> nu_tau (antinu_mu -> antinu_tau) oscillations, respectively. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Delta m^2_{atm} > 0) or with inverted (Delta m^2_{atm} < 0) hierarchy.Comment: 8 pages, 1 figure. Talk given at NOON2004, February 11 - 15, 2004, Tokyo, Japa

Short-Baseline Active-Sterile Neutrino Oscillations?

We suggest the possibility that the anomalies observed in the LSND experiment and the Gallium radioactive source experiments may be due to neutrino oscillations generated by a large squared-mass difference of about 20 - 30 eV^2. We consider the simplest 3+1 four-neutrino scheme that can accommodate also the observed solar and atmospheric neutrino oscillations. We show that, in this framework, the disappearance of nu_e and nu_mu in short-baseline neutrino oscillation experiments is mainly due to active-sterile transitions. The implications of the first MiniBooNE results, appeared after the completion of this paper, are discussed in an addendum.Comment: 12 pages. The implications of the first MiniBooNE results are discussed in an addendu

Determining the Neutrino Mass Hierarchy and CP Violation in NOvA with a Second Off-Axis Detector

We consider a Super-NOvA-like experimental configuration based on the use of two detectors in a long-baseline experiment as NOvA. We take the far detector as in the present NOvA proposal and add a second detector at a shorter baseline. The location of the second off-axis detector is chosen such that the ratio L/E is the same for both detectors, being L the baseline and E the neutrino energy. We consider liquid argon and water-Cherenkov techniques for the second off-axis detector and study, for different experimental setups, the detector mass required for the determination of the neutrino mass hierarchy, for different values of theta13. We also study the capabilities of such an experimental setup for determining CP violation in the neutrino sector. Our results show that by adding a second off-axis detector a remarkable enhancement on the capabilities of the current NOvA experiment could be achieved.Comment: 20 p