Massive neutrinos as probes of fundamental left-right symmetry of nature

Abstract

There are strong indications for neutrino masses and mixings in the data on solar neutrinos as well as in the observed deficit of muon neutrinos from the atmosphere. The COBE data and other analysis of the large scale structure in the Universe also seems to require a hot component in the universe's dark matter, which can be interpreted as a massive neutrino with mass in the few eV range. Implications of a non-vanishing neutrino mass for physics beyond the standard model is discussed. It is argued that a non-zero neutrino mass is a strong indication of a new local B - L symmetry of electro-weak interactions. An elegant extension of the standard model that contains the local B - L symmetry is the left-right symmetric theory of weak interactions. We discuss two versions of it which are motivated by cosmological considerations of baryogenesis and neutrino stability. The first version has a W R mass in the TeV range and can be tested in a wide variety of low energy rare decay experiments including the neutrinoless double beta decay search. The second version arises when the left-right model is embedded into the minimal SO(10) grandunified model. In this case, the low energy values of sin 2θ W and α strong determine the W R mass in the range of 10 9 to 10 12 GeV. An interesting property of the SO(10) embedded version is that the neutrino masses and mixings can be predicted making the minimal SO(10) model testable in the next round of neutrino oscillation experiments. If the parity symmetry is exact down to the scale of B - L symmetry breaking, this model will predict neutrino masses in the eV range and could therefore be tested in the neutrinoless double beta decay experiments.