Is light neutralino as dark matter still viable?
  Motivated by the recent re-confirmation by CoGENT of the low-energy excess of
events observed last year, and the recent improved limits from the XENON-100
experiment that are in contention with the CoGENT data, we re-examine the low
mass neutralino region of the Minimal Supersymmetric Standard Model and of the
Next-to-Minimal Supersymmetric Standard Model, both without assuming gaugino
mass unification. We make several focused scans for each model, determining
conservative constraints on input parameters. We then determine how these
constraints are made increasingly stringent as we re-invoke our experimental
constraints involving the dark matter relic abundance, collider constraints
from LEP and the Tevatron, and then from flavour physics, as a series of
successive 2 sigma hard cuts. We find that for both models, when all relevant
constraints are applied in this fashion, we do not generate neutralino LSPs
that possess a spin-independent scattering cross section in excess of 10^-5 pb
and a mass ~7 GeV < m_chi < ~9 GeV that is necessary in order to explain the
CoGENT observations.
