Radiative decay of a massive particle and the non-thermal process in primordial nucleosynthesis

Abstract

We consider the effects on big bang nucleosynthesis (BBN) of the radiative decay of a long-lived massive particle. If high-energy photons are emitted after the BBN epoch ($t\sim 1-10^3$ sec), they may change the abundances of the light elements through photodissociation processes, which may result in a significant discrepancy between standard BBN and observation. Taking into account recent observational and theoretical developments in this field, we revise our previous study constraining the abundance of the radiatively-decaying particles. In particular, on the theoretical side, it was recently claimed that the non-thermal production of ${}^6$Li, which is caused by the photodissociation of $\text{hefour}$, most severely constrains the abundance of the radiatively-decaying particle. We will see, however, it is premature to emphasize the importance of the non-thermal production of ${}^6$Li because (i) the theoretical computation of the ${}^6$Li abundance has large uncertainty due to the lack of the precise understanding of the ${}^6$Li production cross section, and (ii) the observational data of ${}^6$Li abundance has large errors.

Comments: 15 pages, using REVTeX and 3 postscript figures