Flavor-changing neutral current constraints on standardlike orbifold models

We examine for standardlike orbifold compactification models the constraints due to quark and lepton generation nonuniversality of soft supersymmetry-breaking interactions. We follow the approach initiated by Ibáñez and Lüst and developed by Brignole, Ibáñez, and Muñoz. This is based on a locally supersymmetric σ-model action of moduli and matter fields obeying the stringy duality symmetries. It is assumed that the low energy fields of the minimal supersymmetric standard model are in one-to-one correpondence with string massless modes and that supersymmetry breaking takes place simultaneously with the lifting of flat directions for dilaton and compactification moduli fields. The breaking of supersymmetry is represented in terms of dilaton and moduli auxiliary field components and, consistently with a vanishing cosmological constant, is parametrized in terms of the dilaton-moduli mixing angle θ and the gravitino mass scale ${\mathit{m}}_{\mathit{g}}$. The soft supersymmetry-breaking interactions (gaugino masses, squark and slepton mass matrices, scalar interaction A and B coupling constants) are calculable as a function of these parameters and of the discrete set of molular weight parameters specifying the modular transformation properites of the low energy fields. To establish the flavor-changing neutral current constraints we solve the renormalization group one-loop equations for the full set of gauge, Yukawa, and supersymmetry-breaking coupling constants. A simplified version is used in which one treats the contributions from the third generation quark and lepton Yukawa couplings exactly, while retaining for the first and second generation couplings only the leading order term in the large logarithm variable. Numerical results are obtained for the quantities ${\mathrm{\Delta }}_{\mathit{M}\mathit{N}}$=${\mathit{V}}_{\mathit{M}}$m̃ ${}_{\mathit{M}\mathit{N}}{}^2{}_{}{}^{}$ ${\mathit{V}}_{\mathit{N}}^{\mathrm{°}}$, corresponding to the mass matrices of squarks and sleptons in the super-CKM basis, for which experimental bounds can be determined via the superbox and superpenguin diagrams with gluino or neutralino exchange.