Some aspects of the exotic interactions of neutrinos with an extremely light scalar

We discuss a string-inspired scheme in which an extremely light (or a stric tly massless) scalar particle, coupled very weakly to both neutrinos and to a constituent of the matter, gives rise to neutrino masses within a medium . We also discuss how exotic properties of neutrinos such as possible viola tions of the equivalence principle may produce neutrino oscillations in suc h a scheme. The identification of the scalar with Quintessence is possible if one could avoid a moderate fine-tuning present here as a constraint on t he scalar-neutrino coupling constant from Quintessential cosmology.