A Reexamination of Proton Decay in Supersymmetric Grand Unified Theories

Abstract

We reconsider dimension-five proton decay operators, making semi-quantitative remarks which apply to a large class of supersymmetric GUTs in which the short-distance operators are correlated with the fermion Yukawa couplings. In these GUTs, which include minimal SU(5), the operators $(u^cd_i^c)^\dagger(d_j\nu_\tau)$, induced by charged Higgsino dressing, completely dominate for moderate to large $\tanbeta$. The rate for $p \rarr (K^+,\pi^+) \bar{\nu}_\tau$ grows rapidly, as $\tanbeta^4$, and the K^+ to \pi^+ branching ratio can often be precisely predicted. At small $\tanbeta$ the operators $(u d_i)(d_j \nu)$ are dominant, while the operators $(u d_i)(u \ell^-)$, with left-handed charged leptons, are comparable to the neutrino operators in the generic GUT and suppressed in minimal GUTs. Charged-lepton branching fractions are always small at large $\tanbeta$. The electron to muon ratio is small in minimal GUTs but can be larger, even of order one, in other models. All other operators are very small. At small $\tanbeta$ in non-minimal GUTs, gluino and neutralino dressing effects on neutrino rates are not negligible.