A Common Origin of Asymmetric Self-interacting Dark Matter and Dirac Leptogenesis

We present a framework in which the origin of the baryon asymmetry of the universe is linked to the dynamics of an asymmetric and self-interacting dark sector, while neutrinos remain Dirac fermions. The model extends the Standard Model by introducing three right-handed neutrinos, a pair of dark fermions, and two heavy scalar doublets that mediate interactions between the visible and dark sectors. A global U(1)_B-L symmetry, consistent with a possible ultraviolet gauged completion, ensures the Dirac nature of neutrinos at the renormalisable level. The out-of-equilibrium and CP-violating decays of the heavy scalar doublets generate equal and opposite asymmetries in left-handed and right-handed neutrinos. Because the Yukawa couplings of Dirac neutrinos are tiny, the left–right equilibration occurs only after sphaleron freeze-out, allowing the asymmetry stored in left-handed neutrinos to be partially converted into baryon asymmetry. The same heavy-scalar decays that generate the lepton asymmetry also induce a dark-sector asymmetry, naturally linking the cosmic abundances of visible and dark matter. The dark sector contains a light MeV-scale gauge boson associated with a secluded U(1)_D symmetry. This mediator efficiently depletes the symmetric dark matter component and provides the self-interactions required to address small-scale structure anomalies, while interacting only feebly with the Standard Model through a highly suppressed kinetic portal. The framework offers a coherent and testable connection between Dirac leptogenesis, asymmetric dark matter, and self-interacting dark-sector dynamics.