Abstract
We suggest the existence of a light singlet fermion,
S
, which interacts with observable matter only via a 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
2
3/2
/
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 steaming from superstrings. The
νS
-mixing may be accompanied by observable R-parity breaking effects.