Beyond the Standard Model

The standard model of particle physics is marvelously successful. However, it is obviously not a complete or final theory. I shall argue here that the structure of the standard model gives some quite concrete, compelling hints regarding what lies beyond.Comment: 20 pages, 3 figures available upon request, IAS-HEP 92/2

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

Implications of a Minimal SO(10) Higgs Structure

A minimal SO(10) Higgs structure involving a single adjoint field along with spinors, vectors and singlets has been shown to break the SO(10) gauge symmetry to the standard model while stabilizing the F-flat directions and solving the doublet-triplet splitting problem naturally. With this minimal set of Higgs fields, we show how to construct quark and lepton mass matrices which explain well the many features of the observed spectrum, including the Georgi-Jarlskog mass relations. A large mixing of the muon- and tau-neutrinos results naturally as observed in the atmospheric neutrino data. A particular model relying on a family symmetry has been constructed which realizes the desired mass matrices.Comment: 10 pages, REVTEX, contribution submitted to NEUTRINO 98 Conferenc

Recent Results from the K2K (KEK-to-Kamioka) Neutrino Oscillation Experiment

The latest results of the K2K experiment are reported. The results are based on data taken from June, 1999, to June, 2000, corresponding to a total $2.6 \cdot 10^{19}$ protons on target. Twenty seven fully-contained events in the 22.5 kton fiducial volume of Super-Kamiokande (SK) are observed. The expected number of events is estimated to be 40.3^{+4.7}_{-4.6} assuming the null oscillations hypothesis.Comment: 7 pages, 7 figures. Talk given at the Sixth International Workshop on Tau Lepton Physics, Victoria, BC, Canada, September 19, 200

Matter Effects in Atmospheric Neutrino Oscillations

The Kamiokande II and IMB data on contained events induced by atmospheric neutrinos exhibit too low a ratio of muons to electrons, which has been interpreted as a possible indication of neutrino oscillations. At the same time, the recent data on upward--going muons in underground detectors have shown no evidence for neutrino oscillations, strongly limiting the allowed region of oscillation parameter space. In this paper we confront different types of neutrino oscillation hypotheses with the experimental results. The matter effects in $\nu_\mu \leftrightarrow \nu_e$ and in $\nu_\mu \leftrightarrow \nu_{sterile}$ oscillations are discussed and shown to affect significantly the upward--going muons.Comment: LaTeX, 13 pages, 4 figures (appended as postscript file in the end of the paper, one should cut them and process separately), Roma n. 91

Bounds on Dark Matter from the ``Atmospheric Neutrino Anomaly''

Bounds are derived on the cross section, flux and energy density of new particles that may be responsible for the atmospheric neutrino anomaly. $4.6 \times 10^{-45} cm^2 < \sigma <2.4 \times 10^{-34} cm^2$ Decay of primordial homogeneous dark matter can be excluded.Comment: 10 pages, TeX (revtex

The geometry of atmospheric neutrino production

The zenith angle distributions of atmospheric neutrinos are determined by the possible presence of neutrino oscillations and the combination of three most important contributions: (1) geomagnetic effects on the primary cosmic rays, that suppress the primary flux in the Earth's magnetic equatorial region, (2) the zenith angle dependence of the neutrino yields, due to the fact that inclined showers produce more neutrinos, and (3) geometrical effects due to the spherical shell geometry of the neutrino production volume. The last effect has been recognized only recently and results in an important enhancement of the flux of sub--GeV neutrinos for horizontal directions. In this work we discuss the geometrical effect and its relevance in the interpretation of the atmospheric neutrino data.Comment: 26 pages, 11 figure

Other Atmospheric Neutrino Experiments

The history and recent progress of atmospheric neutrinos are reviewed. An emphasis is placed on results from experiments other than Super-Kamiokande.Comment: 8 pages, 10 figures, Contribution to Neutrino 200

Standard and exotic interpretations of the atmospheric neutrino data

The present status of some theoretical interpretations of the atmospheric neutrino deficit is briefly discussed. Specifically, we show the results for the FC mechanism and for the standard oscillation hypothesis, both in the active and in the sterile channels. All these mechanisms are able to fit the present data to a good statistical level. Among them, the nu_mu --> nu_tau oscillation is certainly the best explanation to the atmospheric neutrino deficit, providing a remarkably good agreement with the data.Comment: 3 pages, 2 figures, talk delivered at the 6th International Workshop on Topics in Astroparticle and Underground Physics (TAUP 99), September 1999, Paris, (to appear in the Conference Proceedings, Nucl. Phys. B (Proc. Suppl.), eds. M. Froissart, J. Dumarchez and D. Vignaud

Possible Effects of Quantum Mechanics Violation Induced by Certain Quantum Gravity on Neutrino Oscillations

In this work we tried extensively to apply the EHNS postulation about the quantum mechanics violation effects induced by the quantum gravity of black holes to neutrino oscillations. The possibilities for observing such effects in the neutrino experiments (in progress and/or accessible in the near future) were discussed. Of them, an interesting one was outlined specially.Comment: 18 pages, 0 figure, (1 REVTeX file