Radiative decay of a massive particle and the nonthermal process in primordial nucleosynthesis

Abstract

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