Neutrino masses and a low breaking scale of left-right symmetry

Abstract

In left-right symmetric models (LRSMs) the light neutrino masses arise from two sources: the seesaw mechanism and a vacuum expectation value of an $\mathrm{SU}{(2)}_{L}$ triplet. If the left-right symmetry breaking ${v}_{R}$ is low, ${v}_{R}\ensuremath{\lesssim}15 \mathrm{TeV},$ the contributions to the light neutrino masses from both the seesaw mechanism and the triplet Yukawa couplings are expected to be well above the experimental bounds. We present a minimal LRSM with an additional U(1) symmetry in which the masses induced by the two sources are below the eV scale and the twofold problem is solved. We further show that, if the U(1) symmetry is also responsible for the lepton flavor structure, the model yields a small mixing angle within the first two lepton generations.