Conclusions

• There is no compelling laboratory evidence for neutrino mass.
• However, neutrino masses are non-zero in most extensions of the standard model, typically , where v = 246 GeV is the weak scale. Thus, probing small neutrino masses indirectly probes the large mass scales of new physics.

• A deficit of solar neutrinos is observed in four experiments. The less serious solar neutrino problem is the deficit of neutrinos, which could well be accounted for by small changes in the astrophysics. Much more serious is that any two of the three classes of experiments can be combined to indicate that the dominant suppression is in the middle of the spectrum, in particular of the neutrinos and the lower energy part of the neutrinos. This is incompatible with any known astrophysical or nuclear physics explanation, suggesting either non-standard neutrino properties or that some of the experiments are wrong. On the other hand, the MSW oscillations give a perfect description of the data. Detailed MSW analyses, including the Earth effect, the day/night asymmetry data, theoretical uncertainties, and their correlations indicate that there are two parameter solutions, both in the general range expected from grand unification, although the details are model dependent. One can also simultaneously determine the MSW and solar parameters. One finds a core temperature , in remarkable agreement with the standard model expectation . Alternately, one can constrain the boron neutrino flux, yielding , consistent with but slightly higher than the SSM expectation. In the future it should be possible with new experiments to determine the initial pp, , and fluxes, with or without MSW being present, in a model independent way.

• There are also anomalies in the atmospheric ratio produced by cosmic ray interactions in the atmosphere. This could also be a sign of neutrino oscillations.

• The combination of COBE data and the large and small scale distribution of galaxies is hard to account for by pure cold dark matter. One possibility is a component of hot dark matter, such as a neutrino in the 10 eV range.

• The possibilities are very exciting. It is quite possible that neutrino mass will be the first clear break with the standard electroweak model. However, much experimental and theoretical work remains.