Heavy neutrino threshold effects in low energy phenomenology

Abstract

Right-handed neutrinos with mass of O (10 12 − 10 13) GeV are required to implement the see-saw mechanism and generate neutrino masses capable of playing a role in structure formation. Moreover models of fermion masses often relate the Yukawa couplings involving these neutrinos to the up-quark Yukawa couplings. Here we study the effects of such couplings on the radiative corrections to quark masses. We find that b − τ equality at M GUT may still give the correct m b / m τ -ratio at low energies, but only if there is large μ − τ mixing in the charged leptonic sector. We propose specific mass matrix “textures” dictated by a U(1) family symmetry whose structure preserves m b = m τ at M GUT. In these schemes, due to the large ν μ − ν τ mixing, it is possible to give a simultaneous solution to the solar neutrino deficit and the atmospheric neutrino problem.