Persistent Tensions in Big Bang Nucleosynthesis and Windows on New Physics

Physics – Nuclear Physics

Scientific paper

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Cosmology, Nucleosynthesis, Quasars, Cosmology, Big Bang Nucleosynthesis, Quasars

Scientific paper

Now that we know the baryon to photon ratio to 5% from the cosmic microwave background, Big Bang Nucleosynthesis using standard physics predicts the abundances of five light nuclei with no free parameters. The Deuterium to Hydrogen ratio measured towards quasars agrees with the prediction to within 10%, but there has been tension verging on disagreement between the estimates of the primordial abundances of 4He and especially 7Li since 1996. While some recent 4He measurements agree, the large majority of measurements over the last 30 years have been smaller than the predictions. For 7Li, the measurements are sufficiently accurate to show that the 7Li/H in old stars in the halo of our Galaxy is a factor of 3-4 below the predicted ratio. Perhaps stars with a variety of masses have destroyed the same amount of 7Li, or we already have evidence for new physics. Improved measurements of the primordial abundances could lead to a detection of a wide variety of new physics because BBN is sensitive to all four forces. Examples include new particles that were relativistic during BBN, decaying particles that change the abundances after BBN or a large net lepton number for the universe that changed the neutron to proton ratio and hence the abundances.

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