Ultra High Energy particles (in excess of 10 eV, have already been detected on Earth ). The mechanisms of acceleration of particles to such energies is still an unanswered question. Taking advantage of the available cosmic particles, the study of Ultra High Energies could help us, on one hand, to test various models of acceleration mechanisms, and on the other hand, to constrain the different candidate theories which aim at extending the Standard Model up to higher unification scales.
The use of neutrinos to observe the Universe has many intrinsic advantages. Charged particles are sensitive to magnetic fields, at the source, during their transport and in the Galaxy; so, except for those with ultimate energies, they do not point to their emission source. In contrast, neutrinos and photons are insensitive to those magnetic fields. However, high energy photons are absorbed by a few hundred g.cm, when the interaction length of a 1 TeV neutrino is about 250 10 g.cm. Furthermore interactions of Very High Energy photons with the infrared radiation and Cosmic Microwave Background (2.7 K) limit their path length to distances smaller than 100 Mpc.
Because they could originate from a common source, the combined study of both the energy spectra of -rays and neutrinos emitted by cosmic sources is necessary in order to tackle the question of the origin of the highest energy cosmic rays and the nature of the mechanisms capable of producing them.
A variety of -ray detectors are already operating. These detectors allow to explore the GeV region (satellites) and above 200GeV (large arrays and ground based Cherenkov imaging telescopes) [2,3,4]. These detectors have already shown evidence of point-like celestial -ray sources.
As for cosmic neutrinos, a few examples of their detection exist at low energies. Let us mention the detection of the signals of solar neutrinos , below 10MeV, and of neutrinos from the supernova SN1987A , at a few tens of MeV. It is, thus, of major interest to explore the possibility to detect signals at higher energies. Several attempts have been made with underground detectors, part of them devoted to proton decay detection. Due to the modest dimensions of such detectors ( 1000 m), only upper limits on the neutrino luminosities of several celestial bodies were obtained [7,8]. The expected fluxes of high energy neutrinos actually require a km-scale detector (see section ).
A summary of the physics potential and of detector development will
be given here.
See  for a more extended presentation.