A model of light pseudoscalar dark matter

TL;DR

This paper proposes a sub-MeV pseudoscalar as a dark matter candidate within an extended electroweak model, analyzing its production mechanisms and experimental constraints to establish its viability.

Contribution

It introduces a novel sub-MeV pseudoscalar dark matter candidate as a pseudo-Nambu-Goldstone boson in the EW-$ u_R$ model, exploring its production via freeze-in and compatibility with current data.

Findings

The sub-MeV scalar can be a viable FIMP dark matter candidate.

Freeze-out mechanism leads to overabundance, while freeze-in yields correct relic density.

The model's scalar sector aligns with current Higgs data and experimental bounds.

Abstract

The EW-$\nu_R$ model was constructed in order to provide a seesaw scenario operating at the Electroweak scale $\Lambda_{EW} \sim 246$ GeV, keeping the same SM gauge structure. In this model, right-handed neutrinos are non-sterile and have masses of the order of $\Lambda_{EW}$. They can be searched for at the LHC along with heavy mirror quarks and leptons, the lightest of which have large decay lengths. The seesaw mechanism requires the existence of a complex scalar which is singlet under the SM gauge group. The imaginary part of this complex scalar denoted by $A^{0}_s$ is proposed to be the sub-MeV dark matter candidate in this manuscript. We find that the sub-MeV scalar can serve as a viable non-thermal feebly interacting massive particle (FIMP)-DM candidate. This $A_s^0$ can be a naturally light sub-MeV DM candidate due to its nature as a pseudo-Nambu-Goldstone (PNG) boson in the model. We show that the well-studied freeze out mechanism falls short in this particular framework producing DM overabundance. We identify that the freeze in mechanism produce the correct order of relic density for the sub-MeV DM candidate satisfying all applicable constraints. We then discuss the DM parameter space allowed by the current bounds from the direct and indirect searches for this sub-MeV DM. This model has a very rich scalar sector, consistent with various experimental constraints, predicts a $\sim 125$ GeV scalar with the SM Higgs characteristics satisfying the current LHC Higgs boson data.