Modular weights, U(1)ʹs and mass matrices

We derive the scalar mass matrices in effective supergravity models with the standard gauge group augmented by a U(1)F family symmetry. Simple relations between U(1)F charges and modular weights of the superfields are derived and used to express the matrices with a minimum number of parameters. The model predicts a branching ratio for the μ→eγ process close to the present experimental limits.