Detection of cosmic microwave background anisotropy at 1.8 deg: Theoretical implications on inflationary models

Theoretical scenarios for the formation of large-scale structure in the universe are strongly constrained by ARGO (a balloon borne experiment reporting detection of cosmic microwave background (CMB) anisotropy at 1.8 deg) and Cosmic Background Explorer/Differential Microwave Radiometer (COBE/DMR). Here we consider flat hybrid models with either scale invariant or tilted (n not equal to 1) initial conditions. For n less than 1, we take into account the effect of a primordial background of gravitational waves, predicted by power-law inflation scenarios. The main result of our analysis is that the ARGO and COBE/DMR data select a range of values for the primordial spectral index: n = 0.95$^{+0.25$$_-0.15$ (values of n outside this range can be rejected at more than 95\% confidence level). These bounds are basically independent of the cosmological abundance of baryons (at least in the range allowed from primordial nucleosynthesis) and of the ratio of cold to hot dark matter. So, flat, cold, or mixed dark matter models, with scale-invariant initial conditions and a standard recombination history, successfully take into account the CMB anisotropy detected at intermediate and large angular scales. }