Testing the Friedmann equation: The Expansion of the universe during big bang nucleosynthesis

In conventional general relativity, the expansion rate H of a Robertson-Walker universe is related to the energy density by the Friedmann equation. Aside from the present day, the only epoch at which we can constrain the expansion history in a model-independent way is during Big-Bang Nucleosynthesis (BBN). We consider a simple two-parameter characterization of the behavior of H during BBN and derive constraints on this parameter space, finding that the allowed region of parameter space is essentially one-dimensional. We also study the effects of a large neutrino asymmetry within this framework. Our results provide a simple way to compare an alternative cosmology to the observational requirement of matching the primordial abundances of the light elements.

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18 pages, Final version to be published in Phys. Rev. D

98.80.Es
26.35.+c
Friedman model
Hubble constant
light nucleus: production
neutrino antineutrino: asymmetry
general relativity
energy: density
numerical calculations: interpretation of experiments

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