The μ-term in effective supergravity theories

The Higgs mixing term coefficient μeff is calculated in the scalar potential in supergravity theories with string origin, in a model independent approach. A general low energy effective expression is derived, where new contributions are included which depend on the modular weights q1,2 of the Higgs superfields, the moduli and derivative terms. We find that in a class of models obtained in the case of compactifications of the heterotic superstring, the derivative terms are identically zero. Further, the total μeff-term vanishes identically if the sum of the two modular weights q1 + q2 is equal to two. Subleading μ-corrections, in the presence of intermediate gauge symmetries predicted in viable string scenarios, are also discussed.