http://arxiv.org/abs/1609.03551
Direct searches for dark matter (DM) by the LUX and PandaX-II Collaborations employing xenon-based detectors have recently come up with the most stringent limits to date on the elastic scattering of DM off nucleons. For Higgs-portal scalar DM models, the new results have precluded any possibility of accommodating low-mass DM as suggested by the DAMA and CDMS II Si experiments utilizing other target materials, even after invoking isospin-violating DM interactions with nucleons. In the simplest model, SM+D, which is the standard model plus a real scalar singlet named darkon acting as the DM candidate, the LUX and PandaX-II limits rule out DM masses from 5 GeV to about 330 GeV, except a small range around the resonant point at half of the Higgs mass where the interaction cross-section is near the neutrino-background floor. In the THDMII+D, which extends the SM+D by the addition of another Higgs doublet, the region excluded in the SM+D by the direct searches can be recovered due to suppression of the DM effective interactions with nucleons at some values of the ratios of Higgs couplings to the up and down quarks, which make the interactions significantly isospin-violating. However, in either model, if the 125-GeV Higgs boson is the portal between the DM and SM sectors, DM masses less than 50 GeV or so are already ruled out by the LHC constraint on the Higgs invisible decay. In the THDMII+D, if the heavier $CP$-even Higgs boson is the portal, theoretical restrictions from perturbativity, vacuum stability, and unitarity requirements turn out to be important instead and exclude much of the region below 100 GeV. For larger DM masses, the THDMII+D has plentiful parameter space that corresponds to interaction cross-sections under the neutrino-background floor and therefore is likely to be beyond the reach of future direct searches without directional sensitivity.
X. He and J. Tandean
Wed, 21 Sep 16
21/53
Comments: 24 pages, 10 figures
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