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 ∼5-10 GeV dark matter particle with a somewhat large elastic scattering cross section with nucleons (σ∼10−40 cm2). 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 (∼30-70 GeV) singlet-like scalar higgs, h1. 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, a1, with ma1∼mh1 and in which the χ0χ0 and bb¯, ss¯ coupling magnitudes of the h1 and a1 are very similar. In this case, the thermal relic abundance is automatically consistent with the measured density of dark matter if mχ0 is sufficiently small that χ0χ0→bb¯ is forbidden.