Are Diffuse High Energy Neutrinos and Gamma-Rays from Starburst Galaxies Observable?

Abstract

Loeb and Waxman have argued that high energy neutrinos from the decay of pions produced in interactions of cosmic rays with interstellar gas in starburst galaxies would be produced with a large enough flux to be observable. Their model is reexamined here and we obtain an upper limit to the diffuse neutrino flux from starburst galaxies. The upper limit obtained here is a factor of ~5 lower than the flux which they predict. Our predicted neutrino flux would be below the atmospheric neutrino foreground flux at energies below \~300 TeV and therefore would be unobservable. PeV neutrinos from starburst galaxies are also unlikely to be detected. Compared with predicted fluxes from other extragalactic high energy neutrino sources, starburst neutrinos with ~PeV energies would have a flux considerably below that predicted for AGN models. We also estimate an upper limit for the diffuse GeV gamma-ray flux from starburst galaxies to be about two orders of magnitude below the observed gamma-ray background, much less than the background from blazars and more than an order of magnitude below that calculated by Thompson et al.