Neutrino-Modulino Mixing

We suggest an existence of light singlet fermion, S, which interacts with observable matter only via Planck mass suppressed interaction: ∼m_3/2/M_P, where m_3/2 is the supergravity gravitino mass. If the mass of the singlet equals ∼m_3/2²/M_P, then ν_e→S resonance conversion solves the solar neutrino problem or leads to observable effects. The νS 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 νS mixing may be accompanied by observable R-parity breaking effects.