Galactic Antiprotons from Photinos

Stable photinos, the photino being the supersymmetry partner of the photon, can explain both the "missing mass" in galactic halos and the cosmic-ray antiproton spectrum up to the highest energies observed so far. This requires a photino mass around 15 GeV; significantly higher masses are cosmologically disfavored. As a consequence, the observed cosmic-ray antiproton-to-proton ratio is predicted to decrease abruptly just above the measured energy range, at $E=m_{\chi }$. If observed, this striking effect would strongly support the hypothesis that photinos make up the missing matter in our galaxy and also lead to a measurement of the photino mass from cosmic-ray data.