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 $\mathrm{\Delta }M$, the singlet-doublet mixing angle $\sin \theta$, and the DM mass $M_{\mathrm{D}\mathrm{M}}$. 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: $100\mathrm{G}\mathrm{e}\mathrm{V}\lesssim M_{\mathrm{D}\mathrm{M}}\lesssim 750$ GeV and ${10}^{-6}\lesssim \sin \theta \lesssim 0.04$ for $\mathrm{\Delta }M>1$ 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 $100\mathrm{G}\mathrm{e}\mathrm{V}\lesssim M_{\mathrm{D}\mathrm{M}}\lesssim 1750$ GeV and $2\times {10}^{-7}\lesssim \sin \theta \lesssim 0.45$ for $\mathrm{\Delta }M>1$ GeV.