Thermal Leptogenesis in the BNT Model of Neutrino Mass

Abstract

We investigate neutrino mass and thermal leptogenesis in the Babu-Nandi-Tavartkiladze (BNT) model featuring a scalar quadruplet ($\Phi$) and a pair of vector-like fermion triplets ($\Sigma$). In this framework, neutrino masses are generated via an effective dimension-7 operator $LLHH(H^{\dagger}H)/\Lambda^3$ at the tree level and via the dimension-5 operator $LLHH/\Lambda$ at the one-loop level. It naturally accommodates sub-eV neutrino masses even if the new physics scale $\Lambda$ is $\mathcal{O}(\rm TeV)$, thus making the model a compelling target for experimental searches. We explore the viability of thermal leptogenesis in this model, which is distinct from the canonical seesaw-based leptogenesis due to the presence of vector-like fermions. We find that leptogenesis is viable for $M_\Sigma \gtrsim 10^{7}$ GeV for a hierarchical spectrum of fermion triplets. However, in the quasi-degenerate regime, resonant enhancement of the $CP$ asymmetry lowers this scale down to $\mathcal{O}({\rm TeV})$, reconciling successful leptogenesis with the originally motivated TeV-scale phenomenology and testability of the model at colliders.