Naturally small Dirac neutrino masses in supergravity

Abstract

We show that Dirac neutrino masses of the right size can arise from the K\"ahler potential of supergravity. They are proportional to the supersymmetry and the electroweak breaking scales. We find that they have the experimentally observed value provided that the ultraviolet cutoff of the Minimal Supersymmetric Standard Model is between the Grand Unification scale and the heterotic string scale. If lepton number is not conserved, then relatively suppressed Majorana masses can also be present, resulting in pseudo-Dirac neutrino masses.