The Effect of Primordial Perturbations on the Extragalactic Infrared Background

Primordial scale-free density perturbations, such as those predicted by inflation, excite large-scale anisotropies in any extragalactic far-infrared background generated by moderate-redshift sources. For practically all the perturbation spectra of cosmological interest, the anisotropy exhibits a universal dependence gamma exp-1/2 on the angular scale gamma, on the only assumption that the universe is transparent to the radiation. The expected harmonic amplitudes, normalized to the dipole of the cosmic microwave background, only depend on the source properties and on the cosmic density parameter. Many harmonics being excited with expected amplitudes of order 1-10 percent the far-infrared background should be fairly chaotic.