Electromagnetic Dirac Cogenesis

Abstract: We propose a novel cogenesis mechanism by utilising the two-body decay of heavy vector-like fermions to dark matter (DM) $\chi$ and right chiral part of light Dirac neutrino $\nu_R$ via the electromagnetic dipole operator. This leads to generation of asymmetry in dark fermion $\chi$ as well as $\nu_R$ with the latter getting transferred to left-handed lepton doublets via Yukawa interactions with a neutrinophilic Higgs doublet. While lepton asymmetry is converted into baryon asymmetry of the Universe via electroweak sphalerons, the dark fermion asymmetry results in asymmetric dark matter. Since CP asymmetries in lepton and dark sector are equal and opposite due to net lepton number conservation, DM mass is restricted to a fixed value $\sim \mathcal{O}(1)$ GeV. Long-lived nature of DM keeps indirect detection prospects at gamma-ray telescopes alive while thermalised light Dirac neutrinos lead to observable dark radiation at cosmic microwave background (CMB) experiments. Heavy vector-like fermions can be probed at terrestrial experiments via their electromagnetic dipole interactions.