Low Mass Neutralino Dark Matter in the MSSM with Constraints from $B_s\to \mu^+\mu^-$ and Higgs Search Limits

The region of low neutralino masses as low as (5-10) GeV has attracted attention recently due to the possibility of excess events above background in dark matter detectors. An analysis of spin independent neutralino-proton cross sections $\SI$ which includes this low mass region is given. The analysis is done in MSSM with radiative electroweak symmetry breaking (REWSB). It is found that cross sections as large as $10^{-40}$ cm$^2$ can be accommodated in MSSM within the REWSB framework. However, inclusion of sparticle mass limits from current experiments, as well as lower limits on the Higgs searches from the Tevatron, and the current experimental upper limit on $B_s\to \mu^+\mu^-$ significantly limit the allowed parameter space reducing $\SI$ to lie below $\sim 10^{-41}$cm$^2$ or even lower for neutralino masses around 10 GeV. These cross sections are an order of magnitude lower than the cross sections needed to explain the reported data in the recent dark matter experiments in the low neutralino mass region.