LIGHT HIGGSINO DARK-MATTER

Wt reinvestigate the question of whether a light Higgsino-like neutral ino is a viable dark matter candidate. To this end we compute the domi nant one-loop corrections to the masses of the Higgino-like states in the minimal supersymmetric standard model (MSSM), due to loops involvi ng heavy quarks and their superpartners. We also calculate analogous c orrections to the couplings of Higgsino-like neutralinos to Z and Higg s bosons. In the region of parameter space leading to high Higgsino pu rity of the lightest neutralino, these corrections can change the expe cted relic density by up to a factor of 5 in either direction, We conc lude that for favorable choices of soft supersymmetry-breaking paramet ers. a state with more than 99% Higgsino purity could indeed form all cold dark matter in the Universe. In some eases these corrections can also increase the expected cross section for LSP scattering off spinle ss nuclei by up to two orders of magnitude, or reduce it to zero.