Infra-red stable fixed points of R-parity violating Yukawa couplings in supersymmetric models

We investigate the infra-red stable fixed points of the Yukawa couplings in the minimal version of the supersymmetric standard model with R-parity vio lation. Retaining only the R-parity violating couplings of higher generatio ns, we analytically study the solutions of the renormalization group equati ons of these couplings together with the top- and b-quark Yukawa couplings. We show that only the B-violating coupling lambda(233)" approaches a non-t rivial infra-red stable fixed point, whereas all other non-trivial fixed po int solutions are either unphysical or unstable in the infra-red region. Ho wever, this fixed point solution predicts a top-quark Yukawa couplings whic h is incompatible with the top quark mass for any value of tan beta. (C) 19 99 Elsevier Science B.V. All rights reserved.