Unified Origin of Dirac Neutrino and Asymmetric Dark Matter Masses via a Dirac-Type Leptogenesis

TL;DR

This work presents an anomaly-free extension of the Standard Model that unifies the origins of light Dirac neutrino masses, asymmetric dark matter (ADM), and the baryon asymmetry via a Froggatt-Nielsen--like $U(1)_X$ mechanism and a stable dark sector protected by $\mathbb{Z}_4^D$. Neutrino masses arise from a Dirac seesaw with $m_{\nu} \sim \epsilon\delta v_S = \epsilon\delta^2\Lambda$, while the GeV-scale ADM mass is set by the same suppression factors, linking the three hierarchies without introducing extra low-energy scales. Leptogenesis proceeds through out-of-equilibrium decays of heavy Dirac neutrinos, with CP asymmetries generating asymmetries in both the visible and dark sectors under exact lepton-number conservation, so sphalerons convert part of the SM lepton asymmetry into the baryon asymmetry. The model naturally yields a fully asymmetric DM scenario compatible with relic abundance, BBN, and direct-detection constraints, and it makes testable predictions for DM interactions via a one-loop Higgs portal, Higgs invisible decays, and $\Delta N_{\rm eff}$ in the CMB. It also opens avenues for UV completions and DM self-interactions, offering a coherent, experimentally accessible link between neutrino physics, baryogenesis, and dark matter.

Abstract

We propose a simple and unified framework that simultaneously explains the origins of light Dirac neutrino masses, asymmetric dark matter (ADM), and the baryon asymmetry of the Universe. The model is based on an extended $U(1)_X$ Froggatt-Nielsen--like mechanism, which naturally generates suppressed Yukawa couplings and realizes a Dirac seesaw for neutrino masses. An additional $\mathbb{Z}_4$ symmetry stabilizes the dark sector, where chiral fermions charged under $\mathbb{Z}_4$ serve as ADM candidates. Leptogenesis occurs through the out-of-equilibrium decays of heavy Dirac neutrinos, where the generated asymmetry is shared between the visible and dark sectors due to exact lepton-number conservation. The same suppression mechanism that explains the smallness of neutrino masses also determines the GeV-scale ADM mass. Numerical studies demonstrate that a fully asymmetric DM scenario is realized, consistent with relic abundance, Big Bang nucleosynthesis, and direct detection constraints. This framework provides an experimentally testable connection between neutrino physics, dark matter, and baryogenesis within an anomaly-free setup.

Figures (12)

• Figure 1: Heavy neutrino decay channels.
• Figure 2: One-loop diagrams for wave function corrections contributing to lepton and dark matter number asymmetries in the heavy Dirac neutrino decay channels.
• Figure 3: Feynman diagram for the complex scalar $\phi$ or $\phi^*$ pair annihilation process into $\eta_I$.
• Figure 4: Feynman diagram for DM number conversion process whose amplitude is suppressed by $\mathcal{O}(\epsilon^2\delta^2)$.
• Figure 5: Left: Dependence of the decay parameter $K_1$ on $M_1$. Right: Resulting baryon-to-photon ratio $\eta_B$ as a function of $M_1$. The horizontal red dashed line indicates the observed value of $\eta_B$.