TOWARDS A THEORY OF SOFT TERMS FOR THE SUPERSYMMETRIC STANDARD MODEL

We perform a systematic analysis of the soft supersymmetry-breaking terms arising in some large classes of four-dimensional strings. The analysis docs not assume any specific supersymmetry-breaking mechanism but provides a means of parametrizing our ignorance in a way consistent with some known properties of these four-dimensional strings. We introduce a goldstino angle parameter theta which says where the source of supersymmetry-breaking resides, either predominantly in the dilaton sector (sin theta = 1 limit) or in the rest of the chiral fields, notably the moduli (sin theta = 0 limit). All formulae for soft parameters take particularly simple forms when written in terms of this angle. The sin theta = 1 limit is (up to small corrections) universal. As sin theta decreases, the model dependence increases and the resulting soft terms may or may not be universal, depending on the model. General expressions for the soft terms as functions of theta for generic four-dimensional strings are provided. For each given string model, one trades the four soft parameters (M, m, A, B) of the minimal supersymmetric standard model by the two parameters m3/2 (gravitino mass) and sin theta. The role of complex phases and the associated constraints from limits on the electric dipole moment of the neutron are discussed. Also emphasized is the importance of treating the problem of the cosmological constant in a self-consistent manner. Three prototype string scenarios are discussed and their low-energy implications arc studied by imposing appropriate radiative SU(2)L x U(1) breaking. The supersymmetric particle spectra present definite patterns which may be experimentally tested at future colliders.