Status of 3-neutrino and 4-neutrino scenarios

Some aspects of the current neutrino oscillation phenomenology are briefly discussed, with emphasis on the status of mass-mixing parameters relevant for scenarios with three active neutrinos, and with an additional fourth sterile neutrino.Comment: 3 pages (including 1 figure). Talk presented at NOW 2000, 2nd International Europhysics Neutrino Oscillation Workshop (Conca Specchiulla, Otranto, Italy), September 9-16, 2000, to be published in Nucl. Phys. B (Proc. Suppl.

Statistical treatment of detection cross-section uncertainties in the analysis of solar neutrino data

We propose a modification to the standard statistical treatment of the detection cross-section uncertainties in the analysis of solar neutrino data. We argue that the uncertainties of the energy-averaged cross sections of the different neutrino fluxes in the same experiment should be treated as correlated. We show that the resulting allowed regions for the neutrino oscillation parameters are significantly larger than the ones obtained with uncorrelated uncertainties.Comment: 12 pages. Corrected Figures 4 and 5 (vacuum oscillations

Phenomenology of Neutrino Oscillations

We review the status of several phenomenological topics of current interest in neutrino oscillations: (i) Solar neutrino oscillations after the first Sudbury Neutrino Observatory measurements, including both model-independent and model-dependent results; (ii) Dominant nu_mu-->nu_tau oscillations of atmospheric and K2K neutrinos, and possible subdominant oscillations induced by either extra states or extra interactions; and (iii) Four-neutrino scenarios embedding the controversial LSND evidence for oscillations.Comment: 9 pages, including 12 figures. Presented at TAUP 2001: Topics in Astroparticle and Underground Physics, Assergi, Italy, 8-12 Sep. 200

Analysis of oscillations of atmospheric neutrinos

We briefly review the current status of standard oscillations of atmospheric neutrinos in schemes with two, three, and four flavor mixing. It is shown that, although the pure \nu_\mu-->\nu_\tau channel provides an excellent 2\nu fit to the data, one cannot exclude, at present, the occurrence of additional subleading \nu_\mu-->\nu_e oscillations (3\nu schemes) or of sizable \nu_\mu-->\nu_s oscillations (4\nu schemes). It is also shown that the wide dynamical range of energy and pathlength probed by the Super-Kamiokande experiment puts severe constraints on nonstandard explanations of the atmospheric neutrino data, with a few notable exceptions.Comment: Talk at the 19th International Conference on Neutrino Physics and Astrophysics - Neutrino 2000 (Sudbury, Ontario, Canada, 16-21 June 2000

Neutrino Oscillation and CP Violation

We reconsider the meaning of observing CP violation in neutrino oscillation.Comment: Talk given at the NUFACT'00: International Workshop on Muon Storage Ring for a Neutrino Factory, Monterey, California, 22-26 May 2000. Several typographical errors are correcte

Super-Kamiokande atmospheric neutrinos: Status of subdominant oscillations

In the context of the recent (79.5 kTy) Super-Kamiokande atmospheric neutrino data, we concisely review the status of muonic-tauonic flavor oscillations and of the subdominant electron or sterile neutrino mixing, in schemes with three or four families and one dominant mass scale. In the three-family case, where we include the full CHOOZ spectral data, we also show, through a specific example, that ``maximal'' violations of the one-dominant mass scale approximation are not ruled out yet.Comment: 8 pages + 10 figure

Is neutrino decay really ruled out as a solution to the atmospheric neutrino problem from Super-Kamiokande data?

In this paper we do a detailed $\chi^2$-analysis of the 848 days of Super-Kamiokande(SK) atmospheric neutrino data under the assumptions of $\nu_\mu - \nu_\tau$ oscillation and neutrino decay. For the latter we take the most general case of neutrinos with non-zero mixing and consider the possibilities of the unstable component in $\nu_\mu$ decaying to a state with which it mixes (scenario (a)) and to a sterile state with which it does not mix (scenario (b)). In the first case $\Delta m^2$ (mass squared difference between the two mass states which mix) has to be $>$ 0.1 $eV^2$ from constraints on $K$ decays while for the second case $\Delta m^2$ can be unconstrained. For case (a) $\Delta m^2$ does not enter the $\chi^2$-analysis while in case (b) it enters the $\chi^2$-analysis as an independent parameter. In scenario (a) there is \dm averaged oscillation in addition to decay and this gets ruled out at 100.0% C.L. by the latest SK data. Scenario (b) on the other hand gives a reasonably good fit to the data for \dm $\sim 0.001 ~eV^2$.Comment: Version to appear in Astropart. Phy

Four-neutrino mixing solutions of the atmospheric neutrino anomaly

Solutions to the atmospheric neutrino anomaly which smoothly interpolate between nu_mu -> nu_tau and nu_mu -> nu_s oscillations are studied. It is shown that, although the Super-Kamiokande data disfavor the pure nu_mu -> nu_s channel, one cannot exclude sizable amplitude for the nu_mu -> nu_s channel in addition to nu_mu -> nu_tau oscillations.Comment: Talk given at Europhysics Neutrino Oscillation Workshop (NOW2000), Conca Specchiulla, Otranto, Lecce, Ita, 9-16 Sep 200

Solar neutrino oscillations in the quasi-vacuum regime

Motivated by recent experimental data, we study solar neutrino oscillations in the range 10^-10 < delta m^2/E < 10^-7 eV^2/MeV. In this range vacuum oscillations become increasingly affected by (solar and terrestrial) matter effects for increasing delta m^2, smoothly reaching the MSW regime. A numerical study of matter effects in such "quasi-vacuum" regime is performed. The results are applied to the analysis of the recent solar neutrino phenomenology.Comment: 4 pages, 2 figures. Talk given at Europhysics Neutrino Oscillation Workshop (NOW 2000), Conca Specchiulla, Otranto, Lecce, Italy, 9-16 Sep 2000. Figure 2 correcte

Three-flavor solar neutrino oscillations with terrestrial neutrino constraints

We present an updated analysis of the current solar neutrino data in terms of three-flavor oscillations, including the additional constraints coming from terrestrial neutrino oscillation searches at the CHOOZ (reactor), Super-Kamiokande (atmospheric), and KEK-to-Kamioka (accelerator) experiments. The best fit is reached for the subcase of two-family mixing, and the additional admixture with the third neutrino is severely limited. We discuss the relevant features of the globally allowed regions in the oscillation parameter space, as well as their impact on the amplitude of possible CP-violation effects at future accelerator experiments and on the reconstruction accuracy of the mass-mixing oscillation parameters at the KamLAND reactor experiment.Comment: 10 pages + 8 figure