Realistic Neutrinogenesis with Radiative Vertex Correction

TL;DR

This paper introduces a model for light Dirac neutrinos and baryon asymmetry via neutrinogenesis, utilizing radiative vertex corrections to generate CP asymmetry without lepton number violation.

Contribution

It presents a novel neutrinogenesis mechanism where CP asymmetry arises from radiative vertex corrections, extending the standard model with new particles and symmetries.

Findings

CP asymmetry generated without lepton number violation

Baryon asymmetry explained via left-handed lepton asymmetry

Neutrinos acquire small Dirac masses through heavy scale suppression

Abstract

We propose a new model for naturally light Dirac neutrinos and explain the baryon asymmetry of the universe through neutrinogenesis. We extend the standard model with a real singlet scalar, a heavy singlet Dirac fermion and a heavy doublet scalar besides three right-handed neutrinos, respecting lepton number conservation and a Z_2 symmetry. The neutrinos acquire small Dirac masses due to the suppression of the weak scale over the heavy mass scale. As a key feature of our construction, once the heavy Dirac fermion and doublet scalar go out of equilibrium, their decays induce the CP asymmetry from the interference of tree-level processes with the \textit{radiative vertex corrections} (rather than the self-energy corrections). Although there is no lepton number violation, an equal and opposite amount of CP asymmetry is generated in the left-handed and the right-handed neutrinos. The left-handed lepton asymmetry would then be converted to the baryon asymmetry in the presence of the sphalerons, while the right-handed lepton asymmetry remains unaffected.