Dark matter in natural supersymmetric extensions of the Standard Model
  We explore the dark matter sector in extensions of the Minimal Supersymmetric
Standard Model (MSSM) that can provide a good fit to the PAMELA cosmic ray
positron excess, while at the same time addressing the little hierarchy problem
of the MSSM. Adding a singlet Higgs superfield, S, can account for the observed
positron excess, as recently discussed in the literature, but we point out that
it requires a fine-tuned choice for the parameters of the model. We find that
including an additional singlet allows both a reduction of the weak-scale
fine-tuning, and an interpretation of the cosmic ray observations in terms of
dark matter annihilations in the galactic halo. Our setup contains a light
axion, but does not require light CP-even scalars in the spectrum.
