Dark Matter-Driven Low-Scale Leptogenesis via Neutrino Portal

TL;DR

We propose a minimal SM extension with three heavy right-handed neutrinos, a Z_2-odd scalar phi and fermion psi, and neutrino-portal couplings that link leptogenesis to the dark sector. The CP violation arises from both standard loop corrections and dark-sector mediated contributions, including numerous 2→2 scattering channels, enabling successful leptogenesis at TeV-scale N1 without resonant enhancement. The dark sector can develop an initial asymmetry that transfers to the visible sector, unifying the origin of the baryon asymmetry with the dark matter abundance. The viable dark matter realization is a two-component system dominated by co-annihilation between nearly degenerate phi and psi in the few-hundred GeV range. Numerical solutions of the coupled Boltzmann equations identify parameter regions that satisfy the observed BAU and relic density, with distinctive dark-sector signatures potentially accessible at the LHC.

Abstract

We propose a novel framework for low-scale leptogenesis within an extension of the Standard Model (SM) that includes three SU(2) singlet right-handed neutrinos, a singlet charged neutral fermion, and a real scalar field. In this setup, the CP asymmetry arises through a rich interplay of mechanisms, including two-body decays of the lightest right-handed neutrino into leptons and Higgs or into dark-sector particles, as well as multiple 2 -> 2 scattering processes involving visible and dark states. Crucially, the CP-violating phases originate not only from conventional vertex and self-energy corrections but also from novel interference effects mediated by the dark sector, which significantly enrich the sources of asymmetry. A distinctive feature of our model is the direct connection between the dark sector and leptogenesis, providing a unified explanation for both the matter-antimatter asymmetry and DM abundance. This connection leads to enhanced CP violation in neutrino interactions and predicts new dark-sector particles accessible at the LHC.

Figures (10)

• Figure 1: Feynman diagram showing the tree-level co-annihilation process $\phi ~ \psi \to \ell~ h$.
• Figure 2: Feynman diagrams representing the one-loop corrections to the decay $N_1 \to \ell H$ including the dark sector contributions to the self-energy.
• Figure 3: Feynman diagrams representing the one-loop corrections to the decay $N_1 \to \phi ~\psi$.
• Figure 4: Feynman diagrams of the scattering process $\phi ~\psi \to \ell ~ H$ ($i \neq j$).
• Figure 5: Feynman diagrams for the scattering process $\phi^\dagger ~\bar{\psi} \to \ell ~ H$($i \neq j$).