Direct detection rate of heavy Higgsino-like and Wino-like dark matter

Many viable dark matter models contain a WIMP candidate that is a component of a new electroweak multiplet whose mass M is large compared to the electroweak scale m_W. A generic amplitude-level cancellation in such models yields a severe suppression of the cross section for WIMP-nucleon scattering, making it important to assess the impact of formally subleading effects. The power correction of order m_W/M to the heavy WIMP limit is computed for electroweak doublet (Higgsino-like) dark matter candidates, and a modern model of nuclear modifications to the free nucleon cross section is evaluated. Corrections to the pure Higgsino limit are determined by a single parameter through first order in the heavy WIMP expansion. Current and projected experimental bounds on this parameter are investigated. The direct detection signal in the pure Higgsino limit remains below neutrino backgrounds for WIMPs in the TeV mass range. Nuclear corrections are applied also to the heavy Wino case, completing the investigation of combined subleading effects from perturbative QCD, 1/M power corrections, and nuclear modifications.