Constraints from charge and colour breaking minima in the (M+1)SSM

We study the constraints on the parameter space of the supersymmetric stand ard model extended by a gauge singlet, which arise from the absence of glob al minima of the effective potential with slepton or squark vevs. Particula r attention is paid to the so-called "UFB" directions in field space, which are F-flat in the MSSM. Although these directions are no longer F-flat in the (M + 1)SSM, we show that the corresponding MSSM-like constraints on m(0 )/M-1/2 apply also to the (M + I)SSM. The net effect of all constraints on the parameter space are more dramatic than in the MSSM. We discuss the phen omenological implications of these constraints. (C) 1999 Elsevier Science B .V. All rights reserved.