CoGeNT, DAMA, and Light Neutralino Dark Matter
  Recent observations by the CoGeNT collaboration (as well as long standing
observations by DAMA/LIBRA) suggest the presence of a $\sim 5$-10 GeV dark
matter particle with a somewhat large elastic scattering cross section with
nucleons ($\sigma\sim 10^{-40}$ cm$^2$).Within the context of the minimal
supersymmetric standard model (MSSM), neutralinos in this mass range are not
able to possess such large cross sections, and would be overproduced in the
early universe. Simple extensions of the MSSM, however, can easily accommodate
these observations. In particular, the extension of the MSSM by a chiral
singlet superfield allows for the possibility that the dark matter is made up
of a light singlino that interacts with nucleons largely through the exchange
of a fairly light ($\sim$30-70 GeV) singlet-like scalar higgs, $\hi$. Such a
scenario is consistent with all current collider constraints and can generate
the signals reported by CoGeNT and DAMA/LIBRA. Furthermore, there is a generic
limit of the extended model in which there is a singlet-like pseudoscalar
higgs, $\ai$, with $\mai\sim \mhi$ and in which the $\chi^0\chi^0$ and $b\anti
b, s\anti s$ coupling magnitudes of the $\hi$ and $\ai$ are very similar. In
this case, the thermal relic abundance is automatically consistent with the
measured density of dark matter if $\mchi$ is sufficiently small that
$\chi^0\chi^0\to b\anti b$ is forbidden.
