Cross sections, relic abundance, and detection rates for neutralino dark matter

Neutralino annihilation and elastic scattering cross sections are derived which differ in important ways from previous work. These are applied to relic abundance calculations and to direct detection of neutralino dark matter from the galactic halo. Assuming the neutralino is the lightest supersymmetric particle and that it is less massive than the Z^0, we find relic densities of neutralinos greater than 4% of critical density for almost all values of the supersymmetric parameters. We constrain the parameter space by using results from the DESY e^+e^- storage ring PETRA (chargino mass less than 23 GeV) and the ASP detector at the SLAC storage ring PEP, and then assuming a critical density of neutralinos, display event rates in a cryogenic detector for a variety of models. A new term implies ``spin-independent'' elastic scattering even for these Majorana particles and inclusion of propagator momenta increases detection rates by 10--300 % even for pure photinos. Z^0-squark interference leads to very low detection rates for some values of the parameters. The new term in the elastic cross section dominates for heavy, mostly spinless materials and mitigates the negative interference cancellations in light materials, except for the pure photino or pure Higgsino cases where it does not contribute. In general, the rates can be substantially different from the pure photino and pure Higgsino special cases usually considered.