Effect of negatively-charged massive particles on big-bang nucleosynthesis and a solution to the lithium problems

Spectroscopic observations of metal poor halo stars give an indication of a possible primordial plateau of ⁶Li abundance as a function of metallicity similar to that for ⁷Li. The inferred abundance of ⁶Li is ∼1000 times larger than that predicted by standard big bang nucleosynthesis (BBN) for the baryon-to-photon ratio inferred from the WMAP data, and that of ⁷Li is about 3 times smaller than the prediction. We study a possible solution to both the problems of underproduction of ⁶Li and overproduction of ⁷Li in BBN. This solution involves a hypothetical massive, negatively-charged particle that would bind to the light nuclei produced in BBN. The particle gets bound to the existing nuclei after the usual BBN, and a second epoch of nucleosynthesis can occur among nuclei bound to the particles. We numerically carry out a fully dynamical BBN calculation, simultaneously solving the recombination and ionization processes of negatively-charged particles by normal and particle-bound nuclei as well as many possible nuclear reactions among them. It is confirmed that BBN in the presence of these hypothetical particles can solve the two Li abundance problems simultaneously.