Low Scale Leptogenesis in Singlet-Triplet Scotogenic Model

TL;DR

This paper explores low-scale leptogenesis within the singlet-triplet scotogenic model, showing it can occur at TeV scales with suppressed washout effects, and links neutrino mass measurements to leptogenesis testing.

Contribution

It demonstrates the possibility of achieving low-scale leptogenesis at TeV energies in the scotogenic model by introducing a specific heavy fermion hierarchy and suppressed Yukawa couplings.

Findings

Leptogenesis scale can be reduced to TeV range with specific heavy fermion hierarchy.

Suppressed Yukawa couplings lead to small active neutrino masses (~10^{-5} eV).

Additional scalar triplet explains the W-boson mass anomaly.

Abstract

The scotogenic model presents an elegant and succinct framework for elucidating the origin of tiny neutrino masses within the framework of the Standard Model, employing radiative corrections within the domain of the dark sector. We investigate the possibility of achieving low-scale leptogenesis in the singlet-triplet scotogenic model (STSM), where dark matter mediates neutrino mass generation. We initially considered a scenario involving two moderately hierarchical heavy fermions, N and $\Sigma$, wherein the lepton asymmetry is generated by the out-of-equilibrium decay of both particles. Our analysis indicates that the scale of leptogenesis in this scenario is similar to that of standard thermal leptogenesis and is approximately $M_{N,\Sigma}\sim 10^{9}$ GeV, which is comparable to the Type-I seesaw case. Further, we consider the case with three heavy fermions ($N_1$, $N_2$, and $\Sigma$) with the hierarchy $M_{N_{1}} < M_{\Sigma} \ll M_{N_{2}}$, which yields the lower bound on heavy fermions up to 3.1 TeV, therefore significantly reduce the scale of the leptogenesis up to TeV scale. The only prerequisite is suppression in the $N_{1}$ and $\Sigma$ Yukawa couplings, which causes suppressed washout effects and a small active neutrino mass of about $10^{-5}$ eV. This brings about the fascinating insight that experiments aiming to measure the absolute neutrino mass scale can test low-scale leptogenesis in the scotogenic model. Further, the hyperchargeless scalar triplet $\Omega$ provides an additional contribution to mass of the $W$-boson explaining CDF-II result.