Majorana dark matter through a narrow Higgs portal

A bstract We update the parameter space of a singlet Majorana fermion dark matter model, in which the standard particles interact with the dark sector through the mixing of a singlet scalar and the Higgs boson. In this model both the dark matter and the singlet scalar carry lepton number, the latter being a bilepton. The stability of the Majorana fermion is achieved by a supposed Z 2 symmetry. The lepton number symmetry breaking scale, driven by the singlet scalar, is constrained to be within hundreds to thousands of GeV, so as to give a sufficiently abundant Majorana fermion. Relic density, direct detection and invisible Higgs decay are considered in a complementary way, as we contrast our parameter space with the Planck, LUX and LHC bounds. The impacts of the future Higgs self-coupling measurements and of XENON1T detector are also discussed. We find a “narrow” Higgs portal in the sense that large deviations from the standard scalar sector (large mixing and low lepton breaking scale) are very restricted by Higgs data global fit. We perform a systematic study of the allowed parameter space, favored by scalar resonances and degeneracy. One important phenomenological signature of this model is the correlation between the discoveries of a dark matter and a singlet scalar particles. Very light singlet scalars were found disfavored by direct detection, interestingly implying that the Majoron present in our spectrum can hardly be a dark radiation candidate if our scenario addresses the DM issue. This model is very predictive and in the next few years should be completely tested by the experiments.