Seesaw neutrino masses and mixing with extended democracy

In the context of a minimal extension of the Standard Model with three extra heavy right-handed neutrinos, we propose a model for neutrino masses and mixing based on the hipothesis of a complete alignment of the lepton mass matrices in flavour space. Considering a uniform quasi-democratic structure for these matrices, we show that, in the presence of a highly hierarchical right-handed neutrino mass spectrum, the effective neutrino mass matrix, obtained through the seesaw mechanism, can reproduce all the solutions of the solar neutrino problem.Comment: Latex, 3pages. Uses espcrc2.sty. Talk given at the Europhysics Neutrino Oscillation Workshop - NOW 2000. To appear in Nucl. Phys. B, Proceedings Supplement

The MONOLITH project

MONOLITH is a proposed massive (34 kt) magnetized tracking calorimeter at the Gran Sasso laboratory in Italy, optimized for the detection of atmospheric muon neutrinos. The main goal is to establish (or reject) the neutrino oscillation hypothesis through an explicit observation of the full first oscillation swing. The Delta m^2 sensitivity range for this measurement comfortably covers the complete Super-Kamiokande allowed region. Other measurements include studies of matter effects and the NC/CC and anti-nu/nu ratio, the study of cosmic ray muons in the multi-TeV range, and auxiliary measurements from the CERN to Gran Sasso neutrino beam. Depending on approval, data taking with part of the detector could start in 2004. The detector and its performance are described, and its potential later use as a neutrino factory detector is addressed.Comment: 6 pages. Contribution to NUFACT'00 neutrino factory workshop, Monterey, CA, USA, May 22-26, 200

Detection of Accelerator-Produced Neutrinos at a Distance of 250 km

The KEK to Kamioka long-baseline neutrino experiment (K2K) has begun its investigation of neutrino oscillations suggested by atmospheric neutrino observations. Twenty-eight neutrino events have been detected in coincidence with the expected arrival time of the beam in the 22.5 kt fiducial volume of Super--Kamiokande, the far detector at 250 km distance. The expectation is 37.8+3.5-3.8, derived using measurements of neutrino interactions in a near detector and extrapolation using a beam simulation validated by a measurement of pion kinematics after production and focusing. The background is of order 10^-3 events.Comment: 6 pages, 3 embedded figures, LaTeX with RevTeX style, submitted to PRL. This version is As Submitte

Nostos - Spherical TPCs

A new concept, the spherical TPC, presents unique advantages when low energy neutrinos are to be detected. Some of the applications are: a) observation of the e oscillation when emitted by a tritium source ( = 14 keV) in a 10 m radius sphere. This project, baptized NOSTOS, intends to give the mixing angle 13, the Weinberg angle and a much lower limit (< 10-12 ?B) of the neutrino magnetic moment, b) an array of small (radius 2-4 m), cheap spheres scattered around the world would be perfect to monitor extragalactic supernovae, c) detect the spectrum of low energy (pp - 7Be) solar neutrinos.Comment: XIII International Symposium on Very High Energy Cosmic Ray Interactions at the NESTOR Institute - Pylos, Grece, 6-12 Septembre 200

Bound on the tau neutrino magnetic moment from the Super-Kamiokande data

It is shown that recent results from the Super-Kamiokande detector constrain the tau neutrino diagonal magnetic moment to $\mu_{\nu_{\tau}} < 1.3\times 10^{-7} \mu_{B}$ for the case of $\nu_{\mu}\to \nu_{\tau}$ interpretation of the atmospheric neutrino anomaly. It is pointed out that the large magnetic moment of the tau neutrino could affect further understanding of the origin of the anomaly.Comment: 7 pages, LaTex. To appear in Phys.Lett.

(Mis)Understanding the Atmospheric Neutrino Anomaly

The apparent attenuation of muon neutrinos relative to electron neutrinos is a bit too low to be compatible with the most popular values of $\Delta m^{2}$. Fits to $R(E_{\nu})$ favor values of $\Delta m^{2}>0.1$ eV$^{2}$. The fit minimized by the Super Kamioka group in estimating neutrino oscillation parameters neglects systematic errors. The fit is dominated by systematic effects. The data being combined in recent fits may not be compatible since there appear to be significant variations in the properties of the data with time. A simple two component neutrino oscillation with $\Delta m^{2}$ in the range of 10$^{-3}$ to 10$^{-2}$ eV$^{2}$ seems unable to account for the observations.Comment: 7 pages, 3 figures, talk given at the Sixth International Workshop on Tau Lepton Physics, Victoria, BC Canada, September 19, 200

The Solar Neutrino Day/Night Effect in Super-Kamiokande

The time variation of the elastic scattering rate of solar neutrinos with electrons in Super-Kamiokande-I was fit to the day/night variations expected from active two-neutrino oscillations in the Large Mixing Angle region. Combining Super-Kamiokande measurements with other solar and reactor neutrino data, the mixing angle is determined as sin^2theta=0.276+0.033-0.026 and the mass squared difference between the two neutrino mass eigenstates as Delta m^2=7.1+0.6-0.5x10^-5eV^2. For the best fit parameters, a day/night asymmetry of -1.7+-1.6(stat)+1.3-1.2(syst)% was determined from the Super-Kamiokande data, which has improved statistical precision over previous measurements and is in excellent agreement with the expected value of -1.6%.Comment: 3 pages, 4 figures; to appear in the proceedings of the TAUP 2003 conferenc

Inconsistencies in Interpreting the Atmospheric Neutrino Anomaly

We note a discrepancy between the value of R expected on the basis of the muon neutrino angular distribution and the value actually observed. The energy independence of $R$ leads to a fine tuning problem. This may be indicative of some unaccounted for new physics.Comment: 3 pages, 5 figure

The Three Neutrino Scenario

I have discussed in my talk several remaining issues in the standard three-flavor mixing scheme of neutrinos, in particilar, the sign of $\Delta m^2_{13}$ and the leptonic CP violating phase. In this report I focus on two topics: (1) supernova method for determining the former sign, and (2) illuminating how one can detect the signatures for both of them in long-baseline (\gsim 10 km) neutrino oscillation experiments. I do this by formulating perturbative frameworks appropriate for the two typical options of such experiments, the high energy and the low energy options with beam energies of $\sim$ 10 GeV and $\sim$ 100 MeV, respectively.Comment: 6 pages, Latex, 2 figures. Talk presented at Europhysics Neutrino Oscillation Workshop (NOW2000), Otranto, Italy, September 9-16, 200

Making Neutrinos Massive with an Axion in Supersymmetry

The minimal supersymmetric standard model (MSSM) of particle interactions is extended to include three singlet (right-handed) neutrino superfields together with three other singlet superfields. The resulting theory is assumed to be invariant under an anomalous global U(1) (Peccei-Quinn) symmetry with one fundamental mass $m_2$. The soft breaking of supersymmetry at the TeV scale is shown to generate an axion scale $f_a$ of order $m_2$. Neutrino masses are generated by $f_a$ according to the usual seesaw mechanism.Comment: 11 pages, substantially revised with important change