Figure 1: Constraining the parameters of the standard cosmological model. | Nature

Figure 1: Constraining the parameters of the standard cosmological model.

From: Rare isotopic insight into the Universe

Figure 1

The abundances of nuclei produced during Big Bang nucleosynthesis essentially depend on two parameters: the density of normal (baryonic) matter, ΩB,0, and the effective number of neutrino species, Neff. The values of ΩB,0 and Neff can be constrained from measurements of the abundance ratio of deuterium to hydrogen (D:1H) in near-primordial environments (blue regions indicate constrained values obtained from D:1H ratios). Cooke1 proposes a different method for constraining these parameters, using measurements of the ratio of the yet-to-be-determined primordial abundances of helium-3 and helium-4 isotopes (3He:4He; green regions indicate constraints based on measurements of 3He:4He values for meteorites that formed at the same time as the Solar System, 4.6 billion years ago). Taken together, the two approaches constrain ΩB,0 and Neff much more than can either individual approach (orange regions indicate combined constraints). Dark and light shades of the coloured regions indicate confidence limits of 68% and 95%, respectively. ΩB,0 is conventionally expressed as its product with h2, where h is the Hubble parameter divided by 100. (Figure adapted from ref. 1.)

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