Neutrinos as a Diagnostic of High Energy Astrophysical Processes

A leading candidate for the extragalactic source of high energy cosmic rays is the Fermi engine mechanism, in which protons confined by magnetic fields are accelerated to very high energy through repeated scattering by plasma shock fronts. For optically thin sources, a strong connection between the emerging cosmic rays and secondary neutrinos can be established. In this context, we show how existing neutrino flux limits can serve to constrain the crossover energy between Galactic and extragalactic dominance in the cosmic ray spectrum. For a low crossover energy \approx 10^9 GeV, the predicted neutrino fluxes are in the range of discovery of the AMANDA telescope. In the second part of the Letter, we show the feasibility of using the Glashow resonance as a discriminator between the pp and p\gamma interactions in Fermi engines as sources of neutrinos. In particular, we demonstrate how three years of observation at the km^3 IceCube facility can serve as a filter for the dominance of the pp interaction at the source