Proton Stability In Supersymmetric SU(5)

We discuss the issue of proton stability within supersymmetric SU(5) GUT and suggest mechanisms for suppression of baryon number violating dimension five and six operators. The mechanism is based on the idea of split multiplets (i.e. quarks and leptons are not coming from a single GUT multiplet) which is realized by an extension with additional vector-like matter. The construction naturally avoids wrong asymptotic mass relations $\hat{M}_D=\hat{M}_E$. Thus, the long standing problems of the minimal SUSY SU(5) GUT are resolved. On a particular example we show that the considered scenario is compatible with a perturbative gauge coupling unification, and nucleon's (dominant) decay arise through $d=6$ operators with $\tau (p\to \pi^0e^+)\simeq 4.8\cdot 10^{33}$ yrs. The decays through $d=5$ operators give the characteristic signature $\tau (p\to K^+\nu_e)\simeq 0.7\tau (p\to K^0\mu^+) \simeq 1.3\cdot 10^{34}(\sin 2\bt/0.5)^2$ yrs.