Tilted hybrid dark matter models and cosmic microwave background anisotropies

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Abstract
We test tilted hybrid models against the results of the Owens Valleyud Radio Observatory, Advanced Cosmic Microwave Explorer, and ULISSEud experiments on cosmic microwave background (CMB) anisotropy. We analyzeud the data using three different statistics (the chi$^{2$, theud likelihood ratio, and the Bayesian analyses), and we discuss if and whenud we get compatible upper limits to the anisotropy. We found stableud results only by performing a combined analysis of the three experiments.ud In this case the differential, single-subtracted, CMB anisotropy at 3ud deg is bounded to be equal to or less than 34 micro K. This implies anud upper limit to the primordial spectral index: n equal to or less thanud 0.7, or n equal to or less than 0.8 if we consider the presence of aud possible gravitational wave background. We also consider the Schuster etud al. full-band data set, which suggests an anisotropy ofud 26$^+18$$_-12$ micro K (at the 90% confidence level).ud This would imply n approximately = 0.5, or n approximately = 0.6 (withud gravitational waves), and at the 95% confidence level n equal to or lessud than 0.9, or n equal to or less than 1 (with gravitational waves). Weud stress that these estimates of n are basically independent of theud relative fraction of cold and hot dark matter.ud

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