Prospects and Blind Spots for Neutralino Dark Matter
  Using a simplified model framework, we assess observational limits and
discovery prospects for neutralino dark matter, taken here to be a general
admixture of bino, wino, and Higgsino. Experimental constraints can be weakened
or even nullified in regions of parameter space near 1) purity limits, where
the dark matter is mostly bino, wino, or Higgsino, or 2) blind spots, where the
relevant couplings of dark matter to the $Z$ or Higgs bosons vanish
identically. We analytically identify all blind spots relevant to
spin-independent and spin-dependent scattering and show that they arise for
diverse choices of relative signs among $M_1$, $M_2$, and $\mu$. At present,
XENON100 and IceCube still permit large swaths of viable parameter space,
including the well-tempered neutralino. On the other hand, upcoming experiments
should have sufficient reach to discover dark matter in much of the remaining
parameter space. Our results are broadly applicable, and account for a variety
of thermal and non-thermal cosmological histories, including scenarios in which
neutralinos are just a component of the observed dark matter today. Because
this analysis is indifferent to the fine-tuning of electroweak symmetry
breaking, our findings also hold for many models of neutralino dark matter in
the MSSM, NMSSM, and Split Supersymmetry. We have identified parameter regions
at low $\tan \beta$ which sit in a double blind spot for both spin-independent
and spin-dependent scattering. Interestingly, these low $\tan \beta$ regions
are independently favored in the NMSSM and models of Split Supersymmetry which
accommodate a Higgs mass near 125 GeV.
