  It has been proposed that the excess in cosmic ray positrons at approximately
8 GeV, observed on both flights of the HEAT balloon experiment, may be
associated with the annihilation of dark matter within the Milky Way halo. In
this paper we demonstrate how the self-annihilation of neutralino dark matter
within local substructure can account for this excess, and estimate the
annihilation cross-section for several benchmark minimal supersymmetric (MSSM)
models. We also demonstrate the effect on the permitted parameter space as
tidal stripping effects and destruction of substructure by mergers becomes
increasingly severe.
