With Grand Unification Signals in, Can Proton Decay be Far Behind?

Abstract

It is noted that one is now in possession of a set of facts, which may be viewed as the matching pieces of a puzzle ; in that all of them can be resolved by just one idea - that is grand unification. These include : (i) the observed family-structure, (ii) quantization of electric charge, (iii) meeting of the three gauge couplings, (iv) neutrino oscillations; in particular the mass of $\nu_{\tau}$ suggested by SuperK), (v) the intricate pattern of the masses and mixings of the fermions, including the smallness of $V_{cb}$ and the largeness of $\theta^{osc}_{\nu_{\mu}\nu_{\tau}}$, and (vi) the need for $B$-$L$ to implement baryogenesis (via leptogenesis). All these pieces fit beautifully together within a single puzzle board framed by supersymmetric unification, based on SO(10) or a string-unified G(224)-symmetry. The one and the most notable piece of the puzzle still missing, however, is proton decay. A concrete proposal is presented, within a predictive SO(10)/G(224)-framework, that successfully describes the masses and mixings of all fermions, including the neutrinos - with eight predictions, all in agreement with observation. An updated study of proton decay is carried out within this framework, which shows that a conservative upper limit on its lifetime is about (1/2-1)\times 10^34 yrs.