  Moduli are generic in string (M) theory. In a large class of gauge-mediated
Supersymmetry breaking models, the fermionic components of such fields have
very light masses, around the eV scale, and non-negligible mixing with active
neutrinos, of order $10^{-4}$. Consequently, these fermions could play the role
of sterile neutrinos to which active neutrinos oscillate, thus affecting
measurements of solar neutrinos or of atmospheric neutrinos. They could also
provide warm dark matter, thus affecting structure formation.
