Light stops, blind spots, and isospin violation in the MSSM
  In the framework of the MSSM, we examine several simplified models where only
a few superpartners are light. This allows us to study WIMP--nucleus scattering
in terms of a handful of MSSM parameters and thereby scrutinize their impact on
dark matter direct-detection experiments. Focusing on spin-independent
WIMP--nucleon scattering, we derive simplified, analytic expressions for the
Wilson coefficients associated with Higgs and squark exchange. We utilize these
results to study the complementarity of constraints due to direct-detection,
flavor, and collider experiments. We also identify parameter configurations
that produce (almost) vanishing cross sections. In the proximity of these
so-called blind spots, we find that the amount of isospin violation may be much
larger than typically expected in the MSSM. This feature is a generic property
of parameter regions where cross sections are suppressed, and highlights the
importance of a careful analysis of the nucleon matrix elements and the
associated hadronic uncertainties. This becomes especially relevant once the
increased sensitivity of future direct-detection experiments corners the MSSM
into these regions of parameter space.
