HIGGS AND SUPER-HIGGS EFFECTS WITH NATURALLY VANISHING CLASSICAL VACUUM ENERGY

We construct N = 1 supergravity models where the gauge symmetry and su persymmetry are both spontaneously broken, with naturally vanishing cl assical vacuum energy and unsuppressed Goldstino components along gaug e non-singlet directions. We discuss some physically interesting situa tions where such a mechanism could play a role, and identify the break ing of a grand-unified gauge group as the most likely possibility. We show that, even when the gravitino mass is much smaller than the scale m(x) of gauge symmetry breaking, important features can be missed if we first naively integrate out the degrees of freedom of mass O(m(x)), in the limit of unbroken supersymmetry, and then describe the super-H iggs effect in the resulting effective theory. We also comment on poss ible connections with extended supergravities and realistic four-dimen sional string constructions.