Radiative Seesaw Mechanism at Weak Scale

We investigate an alternative seesaw mechanism for neutrino mass generation. Neutrino mass is generated at loop level but the basic concept of usual seesaw mechanism is kept. One simple model is constructed to show how this mechanism is realized. The applications of this seesaw mechanism at weak scale to cosmology and neutrino physics are discussed. Seesaw mechanism [1] is one of the best and simplest ways to understand why neutrino, if massive, is much lighter than the corresponding charged lepton in the same generation. The central idea of the seesaw is to introduce a right-handed neutrino νR, which will couple to lepton doublet through Yukawa coupling. The point is that besides the Yukawa interaction term there is another bare Majorana mass term MR for νR. After the gauge symmetry breaking the Yukawa term will result in a Dirac neutrino mass mD. Therefore the neutrino mass matrix takes the form