Impact of conversion-driven processes on singlet-doublet Majorana dark matter relic

Abstract: The singlet-doublet dark matter model offers a rich framework for exploring the nature of dark matter (DM) through its unique fermion structure. In this model, the important parameters are singlet-doublet mass splitting $Δ{M}$, singlet-doublet mixing angle $\sinθ$, and DM mass $M_{\rm DM}$. If the DM is assumed to be of Dirac nature, then the annihilation, co-annihilation, and conversion driven processes combinedly allows a range of parameter space: $1~{\rm GeV} \lesssim M_{\rm DM}\lesssim750$ GeV and $10^{-6}\lesssim\sinθ\lesssim0.04$ for all $Δ{M}>1$ GeV. While the nature of DM either Dirac or Majorana is not known, in this work we assume the nature of singlet-doublet DM to be of Majorana type and find that the relic density and direct detection can be satisfied in a larger parameter space. In particular, the allowed ranges of DM mass and $\sinθ$ are: $1~{\rm GeV}\lesssim M_{\rm DM}\lesssim1750$ GeV and $2\times10^{-7}\lesssim\sinθ\lesssim0.16$ for all $Δ{M}>1$ GeV.