An Infrared Cutoff Revealed by the Two Years of COBE Observations of Cosmic Temperature Fluctuations

We show that a good fitting to the first two years of observations by the Cosmic Background Explorer Differential Microwave Radiometers of the two-point angular correlation function of cosmic background radiation (CBR) temperature is given by models with a nonzero infrared cutoff kₘᵢₙ in the spectrum of the primordial density perturbations. If this cutoff comes from the finiteness of the universe, say, a topological T3 model, we find kₘᵢₙ~(0.3-1.1)πH₀c with confidence level 95%. Such a nonzero kₘᵢₙ universe would also give a better match to the observations both of the rms quadrupole anisotropy of CBR and of galaxy clustering.