Be-7 charge exchange between Be-7(3+) ion and an exotic long-lived negatively charged massive particle in big bang nucleosynthesis

Abstract

The existence of an exotic long-lived negatively charged massive particle, i.e., X-, during big bang nucleosynthesis can affect primordial light element abundances. In particular, the final abundance of Li-7, mainly originating from the electron capture of Be-7, has been suggested to be made smaller by the Be-7 destruction via the radiative X- capture of Be-7 followed by the radiative proton capture of the bound state of Be-7 and X- (Be-7(X)). We suggest a new route of Be-7(X) formation, that is the Be-7 charge exchange at the reaction of Be-7(3+) ion and X-. The formation rate depends on the number fraction of the Be-7(3+) ion, the charge exchange cross section of Be-7(3+), and the probability that produced excited states Be-7(X)* are converted to the ground state. We estimate respective quantities affecting the Be-7(X) formation rate and find that this reaction pathway can be more important than the ordinary radiative recombination of Be-7 and X-. The effect of the charge exchange reaction is then shown in a latest nuclear reaction network calculation. Quantum physical model calculations for related reactions are needed to precisely estimate the efficiency of this pathway in the future.