From the Trees to the Forest: A Review of Radiative Neutrino Mass Models

Abstract

A plausible explanation for the lightness of neutrino masses is that neutrinos are massless at tree level, with their mass (typically Majorana) being generated radiatively at one or more loops. The new couplings, together with the suppression coming from the loop factors, imply that the new degrees of freedom cannot be too heavy (they are typically at the TeV scale). Therefore, in these models there are no large mass hierarchies and they can be tested using different searches, making their detailed phenomenological study very appealing. In particular, the new particles can be searched for at colliders and generically induce signals in lepton-flavor and lepton-number violating processes (in the case of Majorana neutrinos), which are not independent from reproducing correctly the neutrino masses and mixings. The main focus of the review is on Majorana neutrinos. We order the allowed theory space from three different perspectives: (i) using an effective operator approach to lepton number violation, (ii) by the number of loops at which the Weinberg operator is generated, (iii) within a given loop order, by the possible irreducible topologies. We also discuss in more detail some popular radiative models which involve qualitatively different features, revisiting their most important phenomenological implications. Finally, we list some promising avenues to pursue.

Radiative neutrino mass and Majorana dark matter within an inert Higgs doublet model

“…An interesting features of these class of models is that the scale of new physics can be of order TeV, making them testable at high energy colliders [11,12] (For a review, see Ref. [13]). Moreover, the electroweak phase transition can be strongly first order, an essential ingredient for successful electroweak baryogenesis [14].…”

Lepton number violating phenomenology of d = 7 neutrino mass models

“…Therefore it can fit only hierarchical neutrino mass spectra (normal or inverse), but not a degenerate spectrum. 6 The eigenvalues of eq. (3.2) are:…”

“…(For a recent review on theoretical aspects of neutrino masses see [6].) This suppression could be due to loop factors [7,8], or neutrino masses could be generated by higher order operators [9,10], or both.…”

Multicomponent Dark Matter in Radiative Seesaw Models

“…generation is directly connected to cosmological problems such as baryon asymmetry of the Universe [126] and dark matter [39][40][41][42][43][44][45][46][47][48]. Resent cosmological observations with increasing accuracy [88,[127][128][129] provide useful hints on how to extend the neutrino sector.…”

“…The right-handed neutrino is odd under the Z 2 and becomes a candidate of dark matter (DM). The idea of simultaneous explanation for the neutrino masses via the radiative seesaw mechanism and the stability of DM by introducing an exact discrete symmetry has been discussed in many models (see e.g., and the recent review [47] and references therein).…”