Four-Neutrino Oscillations

It is shown that at least four massive neutrinos are needed in order to accommodate the evidences in favor of neutrino oscillations found in solar and atmospheric neutrino experiments and in the LSND experiment. Among all four-neutrino schemes, only two, with a mass spectrum composed of two pairs of neutrinos with close masses separated by the "LSND gap" of the order of 1 eV, are compatible with the results of all neutrino oscillation experiments. In these two schemes the probability of nu_e transitions into other states, the probability of nu_mu->nu_e transitions and the size of CP violation effects in nu_mu->nu_e transitions are suppressed in long-baseline experiments.Comment: 10 pages. Talk presented at the ICFA/ECFA Workshop "Neutrino Factories based on Muon Storage Rings", nu-Fact'99, Lyon, France, 5-9 July 199

Analysis of the Superkamiokande atmospheric neutrino data in the framework of four neutrino mixings

Superkamiokande atmospheric neutrino data for 990 days are analyzed in the framework of four neutrinos without imposing constraints of Big Bang Nucleosynthesis. It is shown that the wide range of the oscillation parameters is allowed at 90% confidence level (0.1\lsim |U_{s1}|^2+|U_{s2}|^2\le 1).Comment: 5 pages, 3 sets of figures, uses style files of fleqn,espcrc2,epsf. Talk presented at ``nufact00'', Monterey, CA, USA, May 22-26, 200

Four-Neutrino Scenarios

The main features of four-neutrino 3+1 and 2+2 mixing schemes are reviewed, after a discussion on the necessity of at least four massive neutrinos if the solar, atmospheric and LSND anomalies are due to neutrino oscillations. Complete list of references on four-neutrino mixing at http://www.to.infn.it/~giunti/neutrinoComment: 7 pages. Talk presented at NOW 2000, Conca Specchiulla (Otranto, Italy), 9-16 Sep. 200

The Search for Neutrino Oscillations numubar->nuebar with KARMEN

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS. It provides numu's, nue's and numubar's in equal intensities from the pi+ mu+ decay at rest (DAR). The oscillation channel numub->nueb is investigated in the appearance mode with a 56t liquid scintillation calorimeter at a mean distance of 17.7m from the nu source looking for p(nue,e+)n reactions. The cosmic induced background for this oscillation search could be reduced by a factor of 40 due to an additional veto counter installed in 1996. In the data collected through 1997 and 1998 no potential oscillation event was observed. Using a unified approach to small signals this leads to an upper limit for the mixing angle of sin**2(2t) < 1.3x10^{-3} (90%CL) at large Dm**2. The excluded area in (sin**2(2t),Dm**2) covers almost entirely the favored region defined by the LSND numub->nueb evidence.Comment: Proceedings Contribution to Neutrino98 in Takayama, Japan, June 4-9, 1998; 13 pages, including 4 figure

Constraints on long-baseline neutrino oscillations from the results of neutrino oscillation experiments

It is shown that in the two schemes with four massive neutrinos which are compatible with the results of all neutrino oscillation experiments, the probabilities of nu_e disappearance and nu_mu->nu_e appearance in long-baseline experiments are severely constrained.Comment: 7 pages, including 2 figures. Talk presented by C. Giunti at TAUP97, September 7-11, 1997, Laboratori Nazionali del Gran Sasso, Ital

Mass or Gravitationally Induced Neutrino Oscillations? -- A Comparison of \B Neutrino Flux Spectra in a Three--Generation Framework

Both gravitational and mass induced neutrino oscillation mechanisms provide possible resolutions to the Solar Neutrino Problem. The distinguishing feature between the two mechanisms is their dependence on the neutrino energy. We investigate the implications of this by computing the \B neutrino spectrum as determined from each mechanism using a realistic three--flavor evolution model. We find that in the limit of small \tetau mixing angle, the differences are significant enough to observe in future solar neutrino experiments.Comment: 14 pages, latex, epsf, 5 figures; to appear in Phys Lett

Emulsion Chamber with Big Radiation Length for Detecting Neutrino Oscillations

A conceptual scheme of a hybrid-emulsion spectrometer for investigating various channels of neutrino oscillations is proposed. The design emphasizes detection of $\tau$ leptons by detached vertices, reliable identification of electrons, and good spectrometry for all charged particles and photons. A distributed target is formed by layers of low-Z material, emulsion-plastic-emulsion sheets, and air gaps in which $\tau$ decays are detected. The tracks of charged secondaries, including electrons, are momentum-analyzed by curvature in magnetic field using hits in successive thin layers of emulsion. The $\tau$ leptons are efficiently detected in all major decay channels, including \xedec. Performance of a model spectrometer, that contains 3 tons of nuclear emulsion and 20 tons of passive material, is estimated for different experimental environments. When irradiated by the $\nu_\mu$ beam of a proton accelerator over a medium baseline of $\sim 1$ km/GeV, the spectrometer will efficiently detect either the \omutau and \omue transitions in the mass-difference region of $\Delta m^2 \sim 1$ eV$^2$, as suggested by the results of LSND. When exposed to the neutrino beam of a muon storage ring over a long baseline of $\sim$ 10-20 km/GeV, the model detector will efficiently probe the entire pattern of neutrino oscillations in the region $\Delta m^2 \sim 10^{-2}-10^{-3}$ eV$^2$, as suggested by the data on atmospheric neutrinos.Comment: 34 pages, 8 figure

Identification of the nature of reading frame transitions observed in prokaryotic genomes

Our goal was to identify evolutionary conserved frame transitions in protein coding regions and to uncover an underlying functional role of these structural aberrations. We used the ab initio frameshift prediction program, GeneTack, to detect reading frame transitions in 206 991 genes (fs-genes) from 1106 complete prokaryotic genomes. We grouped 102 731 fs-genes into 19 430 clusters based on sequence similarity between protein products (fs-proteins) as well as conservation of predicted position of the frameshift and its direction. We identified 4010 pseudogene clusters and 146 clusters of fs-genes apparently using recoding (local deviation from using standard genetic code) due to possessing specific sequence motifs near frameshift positions. Particularly interesting was finding of a novel type of organization of the dnaX gene, where recoding is required for synthesis of the longer subunit, tau. We selected 20 clusters of predicted recoding candidates and designed a series of genetic constructs with a reporter gene or affinity tag whose expression would require a frameshift event. Expression of the constructs in Escherichia coli demonstrated enrichment of the set of candidates with sequences that trigger genuine programmed ribosomal frameshifting; we have experimentally confirmed four new families of programmed frameshifts