Dirac Leptogenesis Assisted Asymmetric Self-interacting Dark Matter

The nature of neutrinos, whether Dirac or Majorana, is hitherto unknown. Assuming neutrinos to be Dirac, which needs \(B-L\) to be an exact symmetry, we make an attempt to explain the observed proportionality between the relic densities of dark matter (DM) and baryonic matter in the present Universe \({ i.e.,}\,\, \Omega _\textrm{DM} \approx 5\, \Omega _\textrm{B}\) . Assuming the existence of heavy \(SU(2)_L\) scalar doublet \((X = (X^0, X^-)^T )\) in the early Universe, an equal and opposite \(B- L\) asymmetry can be generated among the left-handed ( \(\nu _L\) ) and right-handed ( \(\nu _R\) ) neutrinos by the CP-violating out-of-equilibrium decay \(X^0 \rightarrow \nu _L \nu _R \) since \(B - L\) is an exact symmetry. We ensure that \(\nu _L-\nu _R\) equilibration does not occur until below the electroweak (EW) phase transition during which a part of the lepton asymmetry gets converted to the DM asymmetry through a dimension eight operator, which conserves \(B - L\) symmetry and remains in the thermal equilibrium. The remaining \(B - L\) asymmetry then gets converted to a net B-asymmetry through EW-sphalerons which are active at a temperature above 100 GeV. To alleviate the small-scale anomalies of \(\Lambda \) CDM, we assume the DM to be self-interacting via a light mediator, which not only depletes the symmetric component of the DM but also paves a way to detect the DM at terrestrial laboratories through scalar portal mixing.