Radiative Neutrino Mass in Type III Seesaw Model

TL;DR

This paper investigates how radiative corrections generate tiny neutrino masses in the simplest type III seesaw model, concluding that realistic neutrino masses require a very high seesaw scale near grand unification.

Contribution

It provides a detailed calculation of two-loop radiative neutrino masses in the type III seesaw model and discusses the implications for the scale of new physics.

Findings

Radiative neutrino masses are extremely small at low scales.

To match observed neutrino masses, the seesaw scale must be near grand unification.

Low-energy new physics beyond tiny neutrino masses is unlikely in this model.

Abstract

The simplest type III seesaw model as originally proposed introduces one lepton triplet. It thus contains four active neutrinos, two massive and two massless at tree level. We determine the radiative masses that the latter receive first at two loops. The masses are generally so tiny that they are definitely excluded by the oscillation data, if the heavy leptons are not very heavy, say, within the reach of LHC. To accommodate the data on masses, the seesaw scale must be as large as the scale of grand unification. This indicates that the most economical type III model would entail no new physics at low energies beyond the tiny neutrino masses.