We derive model-independent, “naturalness” upper bounds on the magnetic moments ${\mu }_{\nu }$ of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find that current information on neutrino mass implies that $|{\mu }_{\nu }|\lesssim {10}^{-14}\mathrm{bohr}$ magnetons. This bound is several orders of magnitude stronger than those obtained from analyses of solar and reactor neutrino data and astrophysical observations.

• Received 26 April 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.151802