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

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 the singlet-doublet mass splitting $\Delta{M}$, the singlet-doublet mixing angle $\sin\theta$, and the DM mass $M_{\rm DM}$. If the DM is assumed to be of Dirac nature, then the annihilation, co-annihilation, and conversion driven processes combined allow a range of parameter space: $100~{\rm GeV} \lesssim M_{\rm DM}\lesssim750$ GeV and $10^{-6}\lesssim\sin\theta\lesssim0.04$ for $\Delta{M}>1$ GeV. While the nature of DM, either Dirac or Majorana, is not known, in this work, we assume the singlet-doublet DM to be of Majorana type and find that the relic density and direct detection can be satisfied over a larger parameter space. In particular, the allowed ranges of DM mass and $\sin\theta$ are $100~{\rm GeV}\lesssim M_{\rm DM}\lesssim1750$ GeV and $2\times10^{-7}\lesssim\sin\theta\lesssim0.45$ for $\Delta{M}>1$ GeV.