The Link Between Neutrino Masses and Proton Decay in Supersymmetric Unification

One major goal of this talk will be to stress that supersymmetric unification based on symmetries like SO(10) [15], or (for most purposes) a stringderived [6, 16] G(224) = SU(2)L × SU(2)R × SU(4)C, has implications not only for (i) gauge coupling unification and (ii) proton decay, but also for (iii) the masses and mixings of the charged fermions, as well as for (iv) those of the neutrinos. In fact, within a unified theory, all four features (i)–(iv) get intimately linked to each other, much more so than commonly thought. Each of these, including even charged fermion and neutrino-masses, provides some essential clue to the nature of higher unification. As regards the link between the four features, even neutrino masses turn out to have direct influence on proton decay. This is because the latter receives important contributions through a new set of d= 5 operators that depend directly on the Majorana masses of the right-handed neutrinos [17]. These new d= 5 operators, which were missed in the literature, contribute significantly to proton decay amplitudes, in addition of course to the “standard” d= 5 operators [11], which arise through the exchange of the color-triplet Higgsinos related to the electro-weak doublets. The standard and the new d= 5 operators, related to the charged fermion as well as the neutrino masses, together raise our expectation that proton decay should be observed in the near future [18].