Neutralino dark matter after LEP 200

Abstract

I discuss some possible implications from LEP 200 on the lightest neutralino of the minimal supersymmetry, especially as a candidate for the dark matter in the Universe. I show that a non-discovery of a chargino would essentially rule out higgsino-like neutralinos below mw, which are already strongly disfavored by naturalness, and place a rather mild lower bound of about 40 GeV on the mass of gaugino-like neutralinos. Even one charged sfermion with mass below about 80 GeV, if discovered at LEP 200, would imply a deficit of the neutralino relic abundance in the flat Universe in the natural regions of the parameter space. Thus, the cosmologically favored range of sfermion masses lies beyond the reach of LEP 200.