Probing Scalar Dark Matter with Direct Experimental Searches and the LHC

The standard model (SM) plus a real gauge-singlet scalar field called darkon (SM+D) is the simplest model possessing a weakly interacting massive particle (WIMP) dark-matter candidate. The upper limits for the WIMP-nucleon elastic cross-section as a function of WIMP mass recently set by the direct-search experiments XENON10 and CDMS II rule out darkon mass ranges from 10 to (50, 70, 75) GeV for Higgs-boson masses of (120, 200, 350) GeV, respectively. This may exclude the possibility of the darkon providing an explanation for the gamma-ray excess observed in the EGRET data. It is shown that by extending the SM+D to a two-Higgs-doublet model plus a darkon the experimental constraints on the WIMP-nucleon interactions can be evaded due to suppression occurring in some of the parameter space of the model. Moreover, the darkon model can also be probed in Higgs-boson searches at the CERN Large Hadron Collider (LHC).