This conference will address the current issues in neutrino physics and astrophysics. The neutrinos, discovered 45 years ago, are still in many respects mysterious particles. We know they exist in 3 different species, but we don't know if these particles are really massive. Many experiments and projects try to answer this question, using different neutrino sources:

• radioactive nuclei, studied by nuclear physicists
• accelerator neutrinos, studied by particle physicists
• neutrinos from the Sun, or from deeper space (for example supernovae), interesting both physicists and astrophysicists
• neutrinos created by cosmic rays in the atmosphere....

The program of the conference is articulated around 5 themes (1 per day)

1.

The first day is devoted to atmospheric neutrinos and neutrino telescopes. A review will be given of the present results on atmospheric neutrinos, for which the Super-Kamiokande collaboration has found an anomalous composition in the different neutrino species, which could be a consequence of the possibility for massive neutrinos to change their nature (they "oscillate" between different species). This result depends on our understanding of the production of these neutrinos in the atmosphere, which is the subject of the second talk. The third talk will review the current projects aiming at using neutrinos from outer space to draw a map of the sky in neutrinos, opening a totally new window to observational astronomy, and hopefully shed light on the violent mechanisms at work in the Universe ( for example in the active galactic nuclei) which are responsible for the highest energy cosmic rays.

2.

The second theme is focused on the neutrinos from stars. First, two reviews will be given on present results and on future projects on the detection of neutrinos from our Sun: there are strong indications of an apparent deficit in the neutrino flux, which could also be explained by the phenomenon of neutrino oscillations. A review on solar models will give the present state of the art and the necessary progress to fully understand neutrino production in stars. Supernovae explosions are a tremendously strong source of neutrinos, detectable on Earth during a few seconds. Such detections would bring invaluable information both on neutrino properties and the explosion dynamics. The last review talk will be devoted to this subject.

3.

The third day will be devoted to the combined analysis of the atmospheric and solar neutrinos experimental results. Phenomenologists will show how they can or cannot be reconciled with the hypothesis of neutrino oscillations and how they can include the results of further experiments. For instance the possible conversion from one species to another of neutrinos produced at the Los Alamos accelerator (LSND) will be reviewed. Another puzzling result from the tritium beta decay experiments will de discussed. The session will then continue with a review of the search for neutrinoless double beta decay including a discussion on the nuclear uncertainties.

4.

The fourth day will be devoted to the so-called long baseline experiments, consisting in sending accelerator neutrino beams in detectors located several hundred kilometers away; such experiments should clearly confirm or infirm the present anomaly seen in atmospheric neutrinos. The emphasis on this subject is justified by the recent decision taken by CERN to build such a beam aimed at the Gran Sasso laboratory in Italy, so that many European physicists will in the coming years take part in this experimental program. Reviews will be given on the European project as well as on similar projects in Japan and in the United States. Longer term projects (so-called neutrino factories, able to deliver even more intense neutrino beams detectable over thousands of kilometers) will be discussed at the end of this session.

5.

Finally, the fifth and last day is devoted to the more theoretical aspects of neutrinos, both in particle physics modern theories and in cosmology. If neutrinos are massive, this mass must be much lighter (by as much as 10 orders of magnitude) than that of other known particles. A natural explanation of this hierarchy gives a glimpse on physics at energies much higher than presently accessible to accelerators. A related theoretical aspect is to see how the whole pattern of neutrino masses an mixing can shed new light on the family symmetries and so-called textures, whose purpose is to summarize the masses and mixing of other known particles. The existence of neutrino mass may have profound cosmological consequences. The most dramatic one is to offer very natural models for a dynamical explanation of why there is more matter than anti-matter in the Universe. The consequences of neutrino masses on the cosmological microwave background might also be accessible to the next generation of satellites. Finally, the measurements that will best help discriminating between theoretical models will be discussed.