Vanishing squark and slepton masses in a class of supergravity models

We study a class of supergravity models where an observable sector is separated from a hidden sector in the superspace density which defines the supergravity Lagrangian. It is shown that soft supersymmetry-breaking mass terms for squarks and sleptons vanish at the tree level if the cosmological constant vanishes. Since their masses are induced by radiative corrections mostly due to gauge interactions, the sfermions with the same gauge-quantum numbers are highly degenerate in mass, which is required for the suppression of the flavor-changing neutral currents. By a numerical calculation, we find that the ${\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}}_L\times {\mathrm{U}\mathrm{}\left(1\right)\mathrm{}}_Y$ gauge symmetry can be broken by quantum corrections for suitable values of the free parameters. Some phenomenological features of this model are investigated. In particular, this model predicts right-handed sleptons below 150 GeV.