Constraining The Early-Universe Baryon Density And Expansion Rate
Abstract
We explore constraints on extensions to the standard models of cosmology and particle physics which modify the early-Universe expansion rate S = H'/H (parametrized by the effective number of neutrinos Nnu). The constraints on Nnu and the baryon density parameter (etaB = nB/ngamma = 10(-10)*eta10) from BBN at 20 minutes are compared with those from the CMB at 400 kyr and LSS at 14 Gyr. BBN provides the strongest constraint on Nnu (1.6 < Nnu < 3.3 at 95% confidence), but a weaker constraint on etaB. The CMB/LSS best constrain the baryon density (5.9 < eta10 < 6.4 at 95% confidence), independent of Nnu, but provide a relatively weak Nnu constraint, consistent with Nnu = 3. Using the best fit values and the allowed ranges of the CMB/LSS-derived parameters to calculate the BBN-predicted primordial abundances yields excellent agreement with the observationally inferred abundance of deuterium and good agreement with 4He, confirming the consistency between the BBN and CMB/LSS results. However, the BBN-predicted abundance of 7Li is high, by a factor of 3 or more. We comment on the value of Nnu and a possible anomaly in the matter power spectrum inferred from observations of the Ly-alpha forest. The good agreement between our BBN and CMB/LSS results permit us to constrain any post-BBN entropy production as well as to limit the production of any non-thermalized relativistic particles and, allow us to combine them finding 95% ranges, 1.8 < Nnu < 3.2 and 5.9 < eta10 < 6.4.