Abstract
We consider the Singlet Majorana fermion dark matter model, in which the standard model 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. We suppose the existence of a $Z_2$ symmetry, remnant of some high energy local symmetry breaking, that stabilizes the Majorana fermion. We analyzed the parameter space of this model and found that the lepton number symmetry breaking scale, drove by the singlet scalar, is constrained to be within hundreds to thousands of GeV, so as to conform with the observed dark matter relic density. Finally, we address the direct detection and invisible Higgs decay complementarity, confronting our model with recent LUX and LHC constraints, as well as XENON1T prospects.
Highlights
Unambiguous positive DM signal was announced by the experiments, but limits were put on its scattering cross-section off nucleon and production rate
We show some plots that clarify the effects of the singlet scalar mass on the WIMP-nucleon scattering cross section, taking into account the points that are excluded by LUX, that will be accessed by XENON1T and that are within the Planck interval
In order to explore the regions of our parameter space allowed by the Planck, LUX and invisible Higgs decay (IHD) results and accessible by XENON1T detector, we will choose values of the free parameters based on the study of the previous section, instead of arbitrary ones
Summary
The model we consider here consists in a singlet Majorana right-handed neutral fermion, NR, as a DM candidate, whose interaction with the SM particles is through a Higgs portal opened by a singlet complex scalar, σ, that mix to the SM Higgs doublet, φ. Its mass is generated from an Yukawa term involving the σ field when it acquires a nonzero vev and breaks the lepton number symmetry These assumptions reduce the number of free parameters in our model, in comparison with the Majorana fermion models we referenced. Since the discovery of a scalar resonance in the CMS and ATLAS experiments at LHC [10, 11], with mass around 125 GeV, and whose interactions indicate it is most probably the SM Higgs boson, we can be sure that this scalar cannot be a singlet under SU(2)L In our case, it has to come from the doublet-like scalar, Rφ, implying that the mixing angle in eq (2.9) has to be small. We discuss the role of each of them in the observables
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