Stringy Origin of Neutrino Masses within the Minimal Supersymmetric Standard Model

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We present a ``gravity-induced'' seesaw mechanism, which accommodates neutrino masses (mν∝ mᵤ²/Mᵢ, with mᵤ the corresponding quark mass and Mᵢ≃ 4×10¹¹ GeV) compatible with the MSW study of the Solar neutrino deficit within the minimal supersymmetric Standard Model (the grand desert with the gauge coupling unification at Mᵤ≃ 2×10¹⁶ GeV). We show that for large radius (R²/α'= O(20)) Calabi-Yau spaces, threshold corrections ensure Mᵤ²=MC²/ O (2R²/α') and the magnitude of the non-renormalizable terms in the superpotential yields Mᵢ= O(e⁻ʳ²/α')MC. Here MC=g× 5.2× 10¹⁷GeV is the scale of the tree level (genus zero) gauge coupling (g) unification.