The Homi Bhabha Lecture Neutrino Physics and Astrophysics

Neutrinos are very elusive particles. Having only weak (and gravitational) interactions they are extremely difficult to detect, but their study has been always extremely rewarding, both for physics and (more recently) astrophysics. In the last several years the progress in neutrino physics has been impressive leading to the discovery, for the first time, of physics of elementary particle phenomena beyond the Standard Theory. We have now a fair knowledge of the main features of neutrino mass-spectrum and mixing, which I’ll review in § 2. In § 3 I’ll describe the next-generation of experiments, which are under construction or concrete planning. While we know that neutrino masses are extremely small, when compared to the other elementary particles, we do not know their absolute values. This is a very difficult experimental problem, which must be attacked with complementary programmes: precision cosmology, beta-decay and double-beta decay experiments, as I’ll discuss in § 4 and § 5. Photons give information on the surface of the astrophysical bodies, such as stars, neutrinos on the contrary come directly from their inner parts, bringing us precious complementary information. Neutrino astronomy has already started with solar neutrinos and detectors sensitive to a Supernova explosion in our Galaxy are ready to detect the neutrino burst (§ 6). Higher energy neutrino telescopes are at the prototype and even construction stages. Unexpected violent phenomena may be observed in the next several years. I’ll discuss these topics in § 7 and 8. Antineutrinos can give information on the inner part of our own planet; neutrino geology has indeed started this summer with the first observation of “geo-neutrinos” by the KamLAND experiment, of which I’ll tell § 9.