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

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 $\left(t\sim 1-{10}^3\sec \right),$ they may change the abundance 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 nonthermal production of ${}^6\mathrm{Li},$ which is caused by the photodissociation of ${}^4\mathrm{He},$ most severely constrains the abundance of the radiatively decaying particle. We will see however, that it is premature to emphasize the importance of the nonthermal production of ${}^6\mathrm{Li}$ because (i) the theoretical computation of the ${}^6\mathrm{Li}$ abundance has a large uncertainty due to the lack of a precise understanding of the ${}^6\mathrm{Li}$ production cross section, and (ii) the observational data of the ${}^6\mathrm{Li}$ abundance has large errors.