Suppressing dimension five operators in general SU(5) models - art. no. 015015

We discuss dimension-5 operators in supersymmetric models containing extra hypercharge-1/3 color triplets. We derive a general formula relating the di mension-5 operator to the color-triplet mass matrix. We show that certain z eros in the triplet mass matrix together with some triplet coupling selecti on rules can lead to the elimination of dimension-5 operators. In particula r we focus on SU(5) models and show that (a) dimension-5 operators can be e liminated in the standard SU(5) model by the introduction of an extra pair of 5 + (5) over bar Higgs representations with specific couplings, (b) flip ped SU(5) models with extra 10 + <(10)over bar> Higgs representations are f ree of dimension-5 operators, and (c) flipped SU(5) models with extra 5 + ( 5) over bar and/or extra 10 + <(10)over bar> Higgs representations can be m ade free of dimension-5 operators for a textured form of the triplet mass m atrix accompanied by constraints on the 5-plet couplings to matter. Our ana lysis is motivated by the recently put forward M-theory phenomenological fr amework that requires a strong string coupling and reintroduces the problem of eliminating dimension-5 operators.