Revised Big Bang Nucleosynthesis with long-lived negatively charged massive particles: impact of new 6Li limits, primordial 9Be nucleosynthesis, and updated recombination rates [CL]

We extensively re-analyze effects of a long-lived negatively charged massive particle, i.e., X-, on big bang nucleosynthesis (BBN). The BBN model with the X- particle was originally motivated by the discrepancy between 6,7Li abundances predicted in standard BBN model and those inferred from observations of metal-poor stars. We reanalyze this model based upon revised upper limits to the observed primordial 6Li abundance, and find that it remains as a possible solution to the 7Li problem as 7Be is destroyed via the recombination with X- followed by radiative proton capture. We calculate precise nonresonant rates for the radiative recombinations of 7Be, 7Li, 9Be, and 4He with X- taking account of respective partial waves of scattering states and respective bound states. The finite sizes of nuclear charge distributions cause deviations in bound and continuum wave functions from those derived assuming that nuclei are point charges. We find that for a heavy X- mass, m_X \gtrsim 100 GeV, the d-wave –> 2P transition is the most important recombination reaction for 7Li and 7,9Be with an X- particle. This fact is completely different from the case of hydrogen-like electronic ions. Our precise nonresonant rate of the 7Be recombination for m_X=1000 GeV is more than 6 times larger than the existing rate. In addition, we suggest a new reaction for 9Be production: the radiative recombination of 7Li and X- followed by the deuteron capture. We then calculate BBN and find that amounts of 7Be destruction depend significantly on the assumed charge distribution of the 7Be nucleus. Finally, the most realistic constraints on the initial abundance and the lifetime of the X- are deduced. Parameter regions for the solution to the 7Li problem are derived. Primordial 9Be abundances are then predicted in the parameter regions which should be detected in future observations of metal-poor stars.

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M. Kusakabe, K. Kim, M. Cheoun, et. al.
Tue, 18 Mar 14