Asymmetric Self-interacting Dark Matter via Dirac Leptogenesis

TL;DR

This paper proposes a model where Dirac neutrinos and asymmetric self-interacting dark matter are generated via leptogenesis, explaining the dark matter-baryon density ratio and addressing small-scale structure issues.

Contribution

It introduces a novel mechanism linking Dirac neutrino mass, leptogenesis, and self-interacting dark matter with a light mediator, connecting cosmological observations to particle physics.

Findings

Relates dark matter and baryon asymmetries through leptogenesis.

Proposes self-interacting dark matter with a light mediator to solve small-scale structure problems.

Suggests potential detection avenues via scalar portal mixing.

Abstract

The nature of neutrinos, whether Dirac or Majorana, is hitherto not known. Assuming that the neutrinos are 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 ${\it i.e.,}\,\, \Omega_{\rm DM} \approx 5\, \Omega_{\rm B}$. 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 in left and right-handed sectors by the CP-violating out-of-equilibrium decay $X^0 \to \nu_L \nu_R$ 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 dark matter asymmetry through a dimension eight operator, which conserves $B-L$ symmetry and is in 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.