Neutrinos in a gravitational background: A test for the universality of the gravitational interaction

In this work we propose an extended formulation for the interaction between neutrinos and gravitational fields. It is based on the parametrized post-Newtonian approach, and includes a violation of the universality of the gravitational interaction which is nondiagonal in weak flavor space. We find new effects that are not considered in the standard scenario for violation of the equivalence principle. They are of the same order as the effects produced by the Newtonian potential, but they are highly directional dependent and could provide a very clean test of that violation. Phenomenological consequences are briefly discussed. [S0556-2821(99)07904-7].