Singlet-doublet Dirac dark matter

We analyze a simple extension of the standard model where the dark matter particle is a Dirac fermion that is a mixture of a singlet and an SU(2) doublet. The model contains only four free parameters: the singlet and the doublet masses and two new Yukawa couplings. Direct detection bounds in this model are very strong and require the dark matter particle to be singletlike. As a result, its relic density has to be obtained via coannihilations with the doublet. We find that the dark matter mass should be below 750 GeV, the singlet-doublet mass difference cannot exceed 9%, and direct detection experiments offer the best chance to probe this scenario. Finally, we also show that this model can effectively arise in well-motivated extensions of the standard model.