Neutrino-modulino mixing

We suggest an existence of light singlet fermion, S, which interacts with observable matter only via Planck mass suppressed interaction: similar to m(3/2)/M-P, where m(3/2) is the supergravity gravitino mass. If the mass of the singlet equals similar to m(3/2)(2)/M-P, then nu(e) --> S resonance conversion solves the solar neutrino problem or leads to observable effects. The nu S mixing changes supernova neutrino fluxes and has an impact on the primordial nucleosynthesis. The singlet S can originate as the supersymmetric partner of the moduli fields in supergravity or low energy effective theory stemming from superstrings. The nu S mixing may be accompanied by observable R-parity breaking effects.