Assessing the Starburst Contribution to the Γ-ray & Neutrino Backgrounds

If cosmic ray protons interact with gas at roughly the mean density of the interstellar medium in starburst galaxies, then pion decay in starbursts is likely to contribute significantly to the diffuse extra-galactic background in both γ-rays and high energy neutrinos. We describe the assumptions that lead to this conclusion and clarify the difference between our estimates and those of Stecker (2006). Detection of a single starburst by GLAST would confirm the significant contribution of starburst galaxies to the extra-galactic neutrino and γ-ray backgrounds. Subject headings: galaxies:starburst — gamma rays:theory, observations — cosmology:diffuse radiation — ISM:cosmic rays — radiation mechanisms:non-thermal