Two groups of cosmic-ray observers have reported unexpectedly large fluxes of high-energy electrons and positrons. Those excesses suggest either that there are undiscovered astrophysical sources such as radio-quiet pulsars surprisingly nearby or that the positrons and electrons are annihilation products of WIMPs—weakly interacting dark-matter particles hundreds of times more massive than the proton. Standard cosmology predicts that dark nonbaryonic matter dominates the material content of the cosmos. But its constituent particles have yet to be identified. The ATIC balloon collaboration, led by John Wefel of Louisiana State University, reports a significant enhancement in the spectrum of cosmic-ray electrons, peaking near 600 GeV (see the figure). The peak suggests that 600-GeV WIMPs of the kind predicted by extradimensional extensions of standard particle theory might be annihilating with each other to create e+e pairs in very dense concentrations of dark matter not far from our solar system. The ATIC...

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