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Keywords:

  • astroparticle physics;
  • Galaxy: halo;
  • quasars: absorption lines;
  • dark ages, reionization, first stars;
  • primordial nucleosynthesis

ABSTRACT

Standard big bang nucleosynthesis (BBN) at the baryon density determined by the microwave anisotropy spectrum predicts an excess of 7Li compared to observations by a factor of 4–5. In contrast, BBN predictions for D/H are somewhat below (but within 2σ of) the weighted mean of observationally determined values from quasar absorption systems. Solutions to the 7Li problem which alter the nuclear processes during or subsequent to BBN often lead to a significant increase in the deuterium abundance consistent with the highest values of D/H seen in absorption systems. Furthermore, the observed D/H abundances show considerable dispersion. Here, we argue that those systems with D/H ≃ 4 × 10−5 may be more representative of the primordial abundance and as a consequence, those systems with lower D/H would necessarily have been subject to local processes of deuterium destruction. This can be accounted for by models of cosmic chemical evolution able to destroy in situ deuterium due to the fragility of this isotope.