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 $k_{min}$ 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 $k_{min}\sim \mathrm{}(0.3-1.1)\mathrm{}\pi \frac{{\mathrm{H}}_0}{c}$ with confidence level 95%. Such a nonzero $k_{min}$ universe would also give a better match to the observations both of the rms quadrupole anisotropy of CBR and of galaxy clustering.