Implications of the Superkamiokande result on the nature of new physics

Abstract

It is remarked that the SuperKamiokande (SK) discovery of $\nu_\mu$ to $\nu_\tau$ (or $\nu_X$)-oscillation, with a $\delta m^2 \approx 10^{-2}-10^{-3} eV^2$ and $sin^2 2 \theta > 0.8$, provides a clear need for the right-handed (RH) neutrinos. This in turn reinforces the ideas of the left-right symmetric gauge structure $SU(2)_L \times SU(2)_R$ as well as SU(4)-color, for which the RH neutrinos are a compelling feature. It is noted that by assuming (a) that B-L and $I_{3R}$, contained in a string-derived $G(224) = SU(2)_L \times SU(2)_R \times SU(4)^c$ or SO(10), break near the GUT-scale, as opposed to an intermediate scale, (b) the see-saw mechanism, and (c) the SU(4)-color relation between the Dirac mass of the tau neutrino and $m_{top}$, one obtains a mass for $\nu^\tau_L$ which is just about what is observed. This is assuming that the SK group is actually seeing $\nu^\mu_L - \nu^\tau_L$ (rather than $\nu_L^\mu - \nu_X$) oscillation. Following a very recent work by Babu, Wilczek and myself, it is furthermore noted that one can quite plausibly obtain a large $\nu_L^\mu-\nu_L^\tau$ oscillation angle, as observed, in spite of highly non-degenerate masses of the light neutrinos: e.g. with $m(\nu_L^\mu)/m(\nu_L^\tau)\approx 1/10-1/20$. Such non-degeneracy is of course natural to see-saw. In this case, $\nu^e_L - \nu^\mu_L$ oscillation can be relevant to the small angle MSW explanation of the solar neutrino puzzle. Implications of the mass of $\nu^\tau_L$ suggested by the SK result, on proton decay are noted. Comments are made at the end on how the SuperKamiokande result supplements the LEP result in selecting out the route to higher unification.