General limit on the relation between abundances of D and Li-7 in big bang nucleosynthesis with nucleon injections

초록

The injections of energetic hadrons could have occurred in the early Universe by decays of hypothetical long-lived exotic particles. The injections induce the showers of nonthermal hadrons via nuclear scattering. Neutrons generated at these events can react with Be-7 nuclei and reduce Be-7 abundance solving a problem of the primordial Li-7 abundance. We suggest that thermal neutron injection is a way to derive a model independent conservative limit on the relation between abundances of D and Li-7 in hadronic energy injection models. We emphasize that an uncertainty in cross sections of inelastic n + p scattering affects the total number of induced neutrons, which determines final abundances of D and Li-7. In addition, the annihilations of antinucleons with He-4 result in higher D abundance and trigger nonthermal Li-6 production. It is concluded that a reduction of Li-7 abundance from a value in the standard big bang nucleosynthesis (BBN) model down to an observational 2 sigma upper limit is necessarily accompanied by an undesirable increase of D abundance up to at least an observational 12 sigma upper limit from observations of quasistellar object absorption line systems. The effects of antinucleons and secondary particles produced in the hadronic showers always lead to a severer constraint. The BBN models involving any injections of extra neutrons are thus unlikely to reproduce a small Li-7 abundance consistent with observations.

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