Light Neutralinos with Large Scattering Cross Sections in the Minimal Supersymmetric Standard Model

Motivated by recent data from CoGeNT and the DAMA annual modulation signal, we discuss collider constraints on MSSM neutralino dark matter with mass in the 5-15 GeV range. Such an LSP would be a Bino with a small Higgsino admixture. Maximization of the DM-nucleon scattering cross section for such a WIMP requires a light Higgs boson with tan beta enhanced couplings. Limits on the invisible width of the Z boson, when combined with Tevatron constraints on Higgs bosons at large tan beta, and the rare decay $B^{\pm} \to \tau \nu$ constrain cross sections to be below $\sigma_n \lesssim 2 \times 10^{-41} {cm}^2$. This indicates a slight local Dark Matter over-density would be necessary to explain the CoGeNT excess. This scenario also requires a light charged Higgs boson, which can give substantial contributions to rare decays such as $b \to s \gamma$ and $t \to b H^+$.