Massive neutrinos

In this report, both the theoretical and experimental aspects of neutrino masses are discussed. In the first part (theoretical) the two-component description of massless spin-half is described, together with the construction of Majorana mass terms. Next, the predictions of grand unified theories concerning neutrino masses are outlined; the simplest theory based on the minimal SU(5) of Georgi and Glashow predicts zero masses while slight generalizations give neutrino masses of about 10 eV with an uncertainty of at least one order of magnitude. Cosmological consequences of massive neutrinos for the mean energy density of the universe are presented, and finally the astrophysics of galactic halos containing neutrinos is addressed. In the second part (experimental) the problems associated with searches for a finite neutrino mass and for neutrino oscillations are reviewed. The effect of a finite neutrino mass on the energy, momentum and spectral shape of charged particles emitted in weak decays is discussed first. Positive evidence for 14 eV <= msub(ν) <= 46 eV has been reported in the study of tritium beta decay. Searches for neutrino oscillations are described next. Accelerator neutrino beams are sensitive to the squared neutrino mass differences deltam2 approx. equal to 1-100 eV2. No evidence for oscillations is seen although several anomalous experimental results have been reported. Experiments at nuclear reactors are sensitive to smaller values of deltam2 >= 0.1 eV2. The experiments with a deuteron target suggest oscillations with a rather large mixing angle and deltam2 approx. equal to 1 eV2. On the other hand experiments with proton targets are either compatible with no oscillations or with oscillations of a smaller amplitude. The phenomenology of the neutrino oxcillations is summarized in the appendix. (orig.)