When Does CMB + BBN = New Physics?

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  • 22 January 2001
Abstract
Recent cosmic microwave background (CMB) results from BOOMERANG and MAXIMA prefer a value of the baryon density which is somewhat higher than that predicted by Big Bang Nucleosynthesis (BBN). One solution to this problem is to postulate new physics for BBN, such as a neutrino chemical potential. However, the need for such new physics, and the discrepancy between BBN and the CMB results, depends on the priors assumed for CMB. We explore several classes of models involving neutrino degeneracy and extra relativistic degrees of freedom to study the sensitivity of "new physics" to the assumed priors. We find that for the set of models we have examined, the conclusion that the CMB preferred baryon density is high is robust, but the magnitude of the neutrino degeneracy required to reconcile the BBN and CMB results is sensitive to the choice of priors.

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