  The MiniBooNE collaboration recently reported further evidence for the
existence of sterile neutrinos, implying substantial mixing with the
left-handed active neutrinos and at a comparable mass scale. I argue that while
sterile neutrinos may arise naturally in large volume string models, they prove
more of a challenge in heterotic-string models that replicate the Grand Unified
Theory structure of the Standard Model matter states. Sterile neutrinos in
heterotic-string models may imply the existence of an additional Abelian gauge
symmetry of order 10-100TeV.
