Three-loop neutrino masses via new massive gauge bosons from E_6 GUT

We propose an SU(3)_C× SU(2)_L × SU(2)_N × U(1)_Y model arising from E_6 grand unified theory. We show that the tiny neutrino masses in this model can be generated at the three-loop involving the SU(2)_N gauge bosons. With Yukawa couplings around 0.01 or larger and TeV-scale SU(2)_N gauge bosons, we show that the neutrino oscillation data can be explained naturally by presenting a concrete benchmark set of input parameters. All new particles are around the TeV scale. Thus our model can be tested at the ongoing/future collider experiments.