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

Possible breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrino-oscillation experiments, such as a proposed experiment at SOUDAN 2 or one at the DUMAND project. Such a breakdown could be detected with sensitivity to the order of $10^{-14}$ or $10^{-15}$. For generic case of neutrino oscillations, it is emphasized that one can identify the spin of the particle which mediates the force causing the oscillation, by investigating the energy spectrum of the outgoing charged leptons. (based on talk presented at the Workshop on General Relativity and Gravitation held at Univ. of Tokyo, January 17-20, 1994)