Constraining the early-Universe baryon density and expansion rate
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Departments of Physics and Astronomy, The Ohio State University, 191 West Woodruff Avenue, Columbus, OH 43210 (United States)
We explore the constraints on those extensions to the standard models of cosmology and particle physics which modify the early-Universe, radiation dominated, expansion rate S{identical_to}H'/H (parameterized by the effective number of neutrinos N{sub {nu}}). The constraints on S(N{sub {nu}}) and the baryon density parameter {eta}{sub B}{identical_to}(n{sub B}/n{sub {gamma}})=10{sup -10}{eta}{sub 10}, derived from big bang nucleosynthesis (BBN, t{approx}20 min), are compared with those inferred from the cosmic microwave background anisotropy spectrum (CMB, t{approx}400 kyr) and large scale structure (LSS, t{approx}14 Gyr). At present, BBN provides the strongest constraint on N{sub {nu}} (N{sub {nu}} = 2.4 {+-} 0.4 at 68% confidence), but a weaker constraint on the baryon density. In contrast, while the CMB/LSS data best constrain the baryon density ({eta}{sub 10} = 6.1{sub -0.1}{sup +0.2} at 68% confidence), independent of N{sub {nu}}, at present they provide a relatively weak constraint on N{sub {nu}} which is, however, consistent with the standard value of N{sub {nu}} = 3. When the best fit values and the allowed ranges of these CMB/LSS-derived parameters are used to calculate the BBN-predicted primordial abundances, there is excellent agreement with the observationally inferred abundance of deuterium and good agreement with {sup 4}He, confirming the consistency between the BBN and CMB/LSS results. However, the BBN-predicted abundance of {sup 7}Li is high, by a factor of 3 or more, if its observed value is uncorrected for possible dilution, depletion, or gravitational settling. We comment on the relation between the value of N{sub {nu}} and a possible anomaly in the matter power spectrum inferred from observations of the Ly-{alpha} forest. Comparing our BBN and CMB/LSS results permits us to constrain any post-BBN entropy production as well as the production of any non-thermalized relativistic particles. The good agreement between our BBN and CMB/LSS results for N{sub {nu}} and {eta}{sub B} permits us to combine our constraints finding, at 95% confidence, 1.8
- OSTI ID:
- 22156653
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2008, Issue 06; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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