Direct detection and CMB constraints on light DM scenario of top quark
  asymmetry and dijet excess at Tevatron
  We study in detail the model by Isidori and Kamenik that is claimed to
explain the top quark forward-backward asymmetry at Tevatron, provide GeV-scale
dark matter (DM), and possibly improve the agreement between data and theory in
Tevatron W+jj events. We compute the DM thermal relic density, the
spin-independent DM-nucleon scattering cross section, and the cosmic microwave
background constraints on both Dirac and Majorana neutralino DM in the
parameter space that explains the top asymmetry. A stable light neutralino is
not allowed unless the local DM density is 3-4 times smaller than expected, in
which case Dirac DM with mass around 3 GeV may be possible, to be tested by the
Planck mission. The model predicts a too broad excess in the dijet distribution
and a strong modification of the missing E_T distribution in W+jj events.
