Charged lepton flavor violating processes in the Grimus-Neufeld model

Charged Lepton Flavour Violating (cLFV) decays constrain the relationship between the neutrino and the scalar sectors of the Grimus-Neufeld model (GNM), an appealing minimal model of neutrino masses. It turns out, that in the scenario, where the seesaw scale is lower than the electroweak one, cLFV is completely defined by the new Yukawa interactions between the additional single heavy Majorana neutrino, the second Higgs doublet and the lepton doublets. Therefore, we derive a useful parameterization for the Yukawa couplings which reproduces by construction the correct PMNS matrix and the correct neutrino masses for both Normal and Inverted ordering at one-loop level. We embed this scenario in the FlexibleSUSY spectrum-generator generator to perform parameter scans. Focusing on the tiny seesaw scale, we show that current mu -> e gamma limits provide significant constraints on the scalar sector, and we evaluate the impact of future cLFV tau-decay searches for the cases of discovery or non-discovery. The tiny seesaw scale makes the neutrino sector and the cLFV processes in the GNM similar to the scotogenic and the scoto-seesaw models, so we provide constraints for these models as well.

Automated summary

In this study, Charged Lepton Flavour Violating (cLFV) decays in the Grimus-Neufeld model (GNM) were investigated. By introducing additional heavy Majorana neutrino, second Higgs doublet and lepton doublets, a useful parameterization for the Yukawa couplings was derived, which reproduces the correct PMNS matrix and neutrino masses at one-loop level. The impact of current mu -> e gamma limits and future cLFV tau-decay searches on the scalar sector was evaluated. It was found that these constraints are significant for the GNM model. The tiny seesaw scale in the GNM model makes its neutrino sector and cLFV processes similar to the scotogenic and scoto-seesaw models, and constraints for these models were also provided.