Lithium in small magellanic cloud: Implications for new physics

Abstract

One of the main tests of the standard hot Big Bang model comes from predictions of abundances of primordial element, which have been synthesized during the epoch of the Big Bang nucleosynthesis. Though there is a general agreement, there is one more and more pressing disagreement that has not yet been resolved predicted primordial lithium abundance is about 4 times higher than what is observed in atmospheres of MilkyWay halo stars at wide range of low metallicities. To test this issue lithium was observed in the interstellar medium in the Small Magellanic Cloud. The measured abundance was found to be barely consistent with the predicted primordial value, but only very little lithium was made in the cosmic-ray interactions. However, unlike the Milky Way, the Small Magellanic Cloud has suffered a significant tidal disruption due to close galactic fly-bys. We point out that in those cases, tidal shocks can give rise to a population of cosmic rays in addition to standard galactic cosmic rays accelerated in supernova shocks. We demonstrate that significant amount of lithium can be produced in such a scenario where a small galaxy is tidally disrupted in close galactic interactions. In the specific case of the Small Magellanic Cloud, this could potentially be sufficient to make its lithium abundance also inconsistent with the predicted primordial value, leaving the new physics as the only remaining solution to this discrepancy.