Photinos from cosmic sources

In supersymmetric (SUSY) theories¹, the photino is the fermion partner of the photon and is expected to be the lightest stable particle. Despite many discussions of the possible production of photinos, and other supersymmetric particles, at existing and proposed accelerators², so far, experiments have only set limits^3,4. We propose here that photinos are produced by sources of ultra-high-energy cosmic rays. We specifically consider Cygnus X-3, which is a powerful source of neutral particles up to 10⁴ TeV (refs 5-8). These are usually assumed to be γ rays, but there is no direct evidence for this, and shower^5,6 and underground^9,10 experiments suggest that there may be another component present. Here we estimate that a photino flux of the order of 10^-14 cm^-2 s^-1 above 10 TeV is possible from a source such as Cyg X-3, under certain conditions, and consider the feasibility of detecting these photinos.