I. INTRODUCTION There is compelling evidence for dark matter (DM) from a variety of astrophysical observations: rotation rates of galaxies, gravitational lensing, and temperature perturbations of the cosmic microwave background (CMB). The WMAP experiment, which measures the CMB, provides the best value for the DM relic density [1], While there are potential hints of DM in cosmic ray anomalies ( e.g. PAMELA [2] and Fermi [3]) and from the annual modulation signal seen by the DAMA/LIBRA collaboration [4, 5], there is currently no measurement which gives conclusive information about the DM’s properties. The identity of the particle responsible for Ω$_{DM}$ remains a mystery. One DM candidate worthy of special attention is the Weakly Interacting Massive Particle (WIMP). The strongest motivation is the so called “WIMP miracle” – a thermally produced, stable particle with a weak scale mass and perturbative couplings will freeze-out with a relic density of the right order of magnitude to constitute the DM [6]. When added to the expectation of new physics at O (TeV) responsible for the stabilization of the weak scale, the WIMP paradigm becomes even more compelling: the new physics often includes novel symmetries, which result in at least one particle being stable on cosmological timescales. If this particle is weakly interacting then it can be WIMP DM. However, this picture turns out to be an over-simplification. Not just any weak scale stable particle will do. If the DM is weakly interacting in the strictest sense – i.e. has full-strength SU (2)$_{L}$ × U (1)$_{Y}$ gauge interactions – then DM may be excluded by existing direct detection (DD) experiments. In particular, a weak-scale Dirac (vector-like) fermion, χ$_{D}$ , with SU (2) interactions (which encompasses the simplest DM model of all, a Dirac neutrino), feels the weak force via the operator: When the coefficient of this operator is typical in size, namely O ( g/ cos θ$_{w}$ ), where g is the SU (2) coupling constant and θ$_{w}$ is the weak mixing angle, it leads to a huge DD signal – experiments constrain the DM mass to be greater than 50 TeV [7]. Furthermore, the thermal relic density for a 50 TeV Dirac neutrino will be far too large to explain the WMAP measurement. Thus, DM at the weak scale requires a strong suppression of this operator. In fact, it is straightforward to eliminate it entirely. If χ is a Majorana spinor, the operator (¯ χ γ µ χ ) Z 0 µ identically vanishes due to the properties of Majorana bilinears. The DM may be Majorana if an SU (2) singlet Majorana fermion mixes with a Dirac state. This mixing can only be accomplished via SU (2) breaking in the WIMP sector, i.e. through a Higgs boson vacuum expectation value (vev). Then the resultant DM particle has a non-zero coupling to 2 O$_{vector}$ = (¯ χ$_{D}$ γ µ χ$_{D}$ ) Z 0 $_{µ}$. (2) Ω$_{DM}$ h 2 = 0 . 1131 ± 0 . 0034 . (1)