Hints of Standard Model Higgs Boson at the LHC and Light Dark Matter
  Searches
  The most recent results of searches at the LHC for the Higgs boson h have
turned up possible hints of such a particle with mass m_h about 125 GeV
consistent with standard model (SM) expectations. This has many potential
implications for the SM and beyond. We consider some of them in the contexts of
a simple Higgs-portal dark matter (DM) model, the SM plus a real gauge-singlet
scalar field D as the DM candidate, and a couple of its variations. In the
simplest model with one Higgs doublet and three or four generations of
fermions, for D mass m_D < m_h/2 the invisible decay h -> DD tends to have a
substantial branching ratio. If future LHC data confirm the preliminary Higgs
indications, m_D will have to exceed m_h/2. To keep the DM lighter than m_h/2,
one will need to extend the model and also satisfy constraints from DM direct
searches. The latter can be accommodated if the model provides sizable isospin
violation in the DM-nucleon interactions. We explore this in a
two-Higgs-doublet model combined with the scalar field D. This model can offer
a 125-GeV SM-like Higgs and a light DM candidate having isospin-violating
interactions with nucleons at roughly the required level, albeit with some
degree of fine-tuning.
