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 does 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 θ which says where the source of supersymmetry-breaking resides, either predominantly in the dilaton sector (sin θ=1 limit) or in the rest of the chiral fields, notably the moduli (sin θ=0 limit). All formulae for soft parameters take particularly simple forms when written in terms of this angle. The sin θ=1 limit is (up to small corrections) universal. As sin θ 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 θ 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 θ. 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 are studied by imposing appropriate radiative SU(2)LxU(1) breaking. The supersymmetric particle spectra present definite patterns which may be experimentally tested at future colliders. ((orig.))