Implications of Muon Anomalous Magnetic Moment for Supersymmetric Dark Matter

The anomalous magnetic moment of the muon has recently been measured to be in conflict with the standard model prediction with an excess of $2.6\sigma$. Taking the excess at face value as a measurement of the supersymmetric contribution, we find that at $95\%$ confidence level it imposes an upper bound of 500 GeV on the neutralino mass and forbids Higgsinos as being the bulk of cold dark matter. Other implications for the astrophysical detection of neutralinos include an accessible minimum direct detection rate, lower bounds on the indirect detection rate of neutrinos from the Sun and the Earth, and a suppression of the intensity of gamma ray lines from neutralino annihilations in the galactic halo.