New constraints on inflation from the cosmic microwave background - art. no. 023505

The recent data from the BOOMERANG and MAXIIMA-1 balloon flights have marke d the beginning of the precision era of cosmic microwave background (CMB) a nisotropy measurements. We investigate the observational constraints from t he current CMB anisotropy measurements on the simplest inflation models, ch aracterized by a single scalar field phi, in the parameter space consisting of scalar spectral index n(S) and tensor/scalar ratio r. If we include con straints on the baryon density from big bang nucleosynthesis (BBN), we show that the favored inflationary models have a negligible tensor amplitude an d a red tilt, with a best fit of n(S)similar or equal to0.93, which is cons istent with the simplest small-held inflation models, but rules out large-h eld models at the 1 sigma level. Without including BBN constraints, a broad er range of models is consistent with the data. The best fit (assuming negl igible reionization) is a scale-invariant spectrum, n(S)similar or equal to 1, which includes large-held and hybrid scenarios. Large-field models (such as those typical of the chaotic inflation scenario) with a tilt n(S)<0.9 a re strongly disfavored in all cases.