Neutrinos with Seesaw Masses and Suppressed Interactions

Abstract

Mixing between light and heavy neutrino states has been proposed as an explanation (or partial explanation) for the 3-sigma NuTeV anomaly and the 2-sigma departure of the $Z^0$ invisible width from its expected value. I assume herein that neutrino masses and mixings result from the conventional seesaw mechanism involving six chiral neutrino states, the first three being members of weak doublets, the others weak singlets. A finely-tuned choice of both the (bare) Majorana masses and the (Higgs-induced) Dirac masses can fit solar and atmospheric neutrino data and also result in significant (but necessarily flavor-dependent) mixing between singlet and doublet states such as would yield detectable suppression of light neutrino interaction amplitudes. The possibility for this kind of suppressive mixing is constrained by the observed upper limit on radiative muon decay.