Implications of the COBE-DMR and South-Pole Experiments on CMB Anisotropies to Inflationary Cosmology

• Published in: Progress of Theoretical Physics
• Main Author: Sasaki, Misao
• Format: Text
• Language: English
• Published: Oxford University Press 1993
• Subjects: Articles; South Pole; South pole
• Online Access: http://ptp.oxfordjournals.org/cgi/content/short/89/6/1183; https://doi.org/10.1143/ptp/89.6.1183

We discuss implications of the discovery of the cosmic microwave anisotropy at 10\degr scale by COBE-DMR and the null result at 1\degr scale from the South-Pole experiment to inflationary universe models. In doing so, we derive an approximate analytic formula which relates the anisotropies at 10\degr and at 1\degr without a heavy numerical computation. The formula, when tested against the known numerical results, turns out to reproduce those results quite accurately, and gives us a clear insight into cause and effect of the intermediate and large angular CMB anisotropies. Then applying the formula to models with adiabatic density perturbations based on the inflationary universe scenario, we find that the only model compatible with the claimed observational data is either (i) a power-law inflation model which predicts the power spectrum of density fluctuations with the power-law index n \lesssim0.8, in which case the gravitational wave contribution to the CMB anisotropies on θ> 5\degr FWHM is significant, or (ii) a natural inflation model with n \lesssim0.7, in which case the gravitational wave contribution is negligible on all angular scales. In both of these cases, if the universe is dominated by cold dark matter, the resulting bias factor turns out to be b \gtrsim2, i.e., a relatively large bias is unavoidable.