A Reexamination of Proton Decay in Supersymmetric Grand Unified Theories

We reconsider dimension–five proton decay operators, making semiquantitative 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 (udi ) (djντ ), induced by charged Higgsino dressing, completely dominate for moderate to large tan β. The rate for p → (K+, π)ντ grows rapidly, as tan4 β, and the K+ to π+ branching ratio can often be precisely predicted. At small tan β the operators (udi)(djν) are dominant, while the operators (udi)(ul ), with left-handed charged leptons, are comparable to the neutrino operators in the generic GUT and suppressed in minimal GUTs. Chargedlepton branching fractions are always small at large tanβ. 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 tan β in nonminimal GUTs, gluino and neutralino dressing effects on neutrino rates are not negligible. Permanent address as of August 1, 1998.