We study the solar neutrino problem within the framework of a parametrized post-Newtonian formulation for the gravitational interaction, which incorporates a violation of the equivalence principle (VEP), and examine the more important VEP effects using the current data on the rates and the energy spectrum. We find two possible solutions for the neutrino rate, one of them involving the MSW effect in matter and the other corresponding to a vacuum oscillation. In both cases, a semi-annual seasonal modulation of the neutrino flux is predicted, because of the anisotropic contributions to the gravitational effects. Our analysis provides new constraints for some VEP parameters.

• Received 15 October 1999

DOI:https://doi.org/10.1103/PhysRevD.61.105004