Scalar-tensor theory of gravitation: Generalizations and experimental limitations

Several theories with scalar field can be derived from different variational principles. Here we consider a very general variational principle and we prove that, in the exterior case without electromagnetic field, the solution for a particular case generates the set of solutions for the general case. This is applied to the exterior solution in the static case with spherical symmetry without electromagnetic field. We investigate the predictions for the classic effects and the event horizons. Then we get some limitations for the variational principles which generalize the usual limitations. In all these cases the Schwarzschild solution with his horizon appears as a very particular case.