Tilted hybrid dark matter models and cosmic microwave background anisotropies

We test tilted hybrid models against the results of the Owens Valley Radio Observatory, Advanced Cosmic Microwave Explorer, and ULISSE experiments on cosmic microwave background (CMB) anisotropy. We analyze the data using three different statistics (the chi2, the likelihood ratio, and the Bayesian analyses), and we discuss if and when we get compatible upper limits to the anisotropy. We found stable results only by performing a combined analysis of the three experiments. In this case the differential, single-subtracted, CMB anisotropy at 3 deg is bounded to be equal to or less than 34 micro K. This implies an upper limit to the primordial spectral index: n equal to or less than 0.7, or n equal to or less than 0.8 if we consider the presence of a possible gravitational wave background. We also consider the Schuster et al. full-band data set, which suggests an anisotropy of 26+18-12 micro K (at the 90% confidence level). This would imply n approximately = 0.5, or n approximately = 0.6 (with gravitational waves), and at the 95% confidence level n equal to or less than 0.9, or n equal to or less than 1 (with gravitational waves). We stress that these estimates of n are basically independent of the relative fraction of cold and hot dark matter.