A test of the equivalence principle by long-baseline neutrino-oscillation experiments

We show that a breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrino-oscillation experiments. In particular we have analyzed in detail a proposed experiment at SOUDAN 2 with $\nu_\mu$ beams from the Fermilab Main Injector. It turns out that we can study both masses of neutrinos and such a breakdown with sensitivity to the order of $10^{-14}$ by investigating the energy spectrum of the resulting muons.