3-Neutrino mass spectrum from combining seesaw and radiative neutrino mass mechanisms

We extend the Standard Model by adding a second Higgs doublet and a right-handed neutrino singlet with a heavy Majorana mass term. In this model, there are one heavy and three light Majorana neutrinos with a mass hierarchy m3≫m2≫m1 such that that only m3 is non-zero at the tree level and light because of the seesaw mechanism, m2 is generated at the one-loop and m1 at the two-loop level. We show that the atmospheric neutrino oscillations and large mixing MSW solar neutrino transitions with Δm2atm≃m32 and Δm2solar≃m22, respectively, are naturally accommodated in this model without employing any symmetry.