Tijana Prodanovic, Tamara Bogdanovic, Dejan Urosevic
Observations of the low-metallicity halo stars have revealed a puzzling result that the abundance of 7Li in these stars is at least three times lower than its predicted primordial abundance. Given the difficulty of lithium observations in stellar atmospheres it is unclear whether this disagreement results from lack of understanding of lithium destruction mechanisms in stars or in non-standard physics behind the Big Bang Nucleosynthesis (BBN). It has been proposed that the uncertainties related to the destruction of lithium in stars can be circumvented by observing lithium in gas phase of low metallicity systems, such as the Small Magellanic Cloud (SMC), where the lithium abundance values are expected to be closer to the primordial. In this work we propose that there may be another mechanism responsible for lithium production in systems like the SMC where cosmic rays can be accelerated in tidal interactions caused by galactic fly-bys. We show that large-scale tidal shocks from a few fly-bys could produce lithium in the amounts comparable to those expected from interactions of the galactic cosmic-rays (GCR) produced in supernovae over the entire history of a system. In the case of the SMC, we find that only two such fly-bys can account for as much lithium as the standard, GCR production channel. However, given that the measured lithium abundance in the SMC is already consistent with the predicted primordial abundance, there is little room for contributions from other sources. Adding a new mechanism for production of lithium, such as the tidal cosmic rays, would cause even more tension with the standard BBN theory, and be more in favor of the non-standard physics as a possible solution to the pressing lithium problem.
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http://arxiv.org/abs/1211.3118
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