  The standard model (SM) plus a real gauge-singlet scalar field dubbed 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 from the recent XENON10 and CDMS-II
experiments 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. We show 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 circumvented due to suppression occurring at
some values of the product tan(alpha)tan(beta), with alpha being the
neutral-Higgs mixing angle and tan(beta) the ratio of vacuum expectation values
of the Higgs doublets. We also comment on the implication of the darkon model
for Higgs searches at the LHC.
