Massive Neutrinos as Probe of Higher Unification

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. Non-zero neutrino mass is a strong indication of a new local $B-L$ symmetry of electro-weak interactions . In particular, it is noted that the simplest picture based on the left-right symmetric unification with a high scale for the $B-L$ symmetry (as well as the scale of the right-handed gauge boson $W_R$) as required by the constraints of grandunification and present LEP data in a minimal $SO(10)$ model, can accomodate the solar neutrino data and a weak hot dark matter neutrino but not the atmospheric neutrino puzzle. A model with low scale $W_R$ ( in the TeV range) where the Dirac mass of the neutrino arises at the one loop level can also do the same job. The low $W_R$ picture can be tested in many rare decay experiments.