Possible solution to the 7Li problem by the long lived stau

Modification of standard big-bang nucleosynthesis is considered in the minimal supersymmetric standard model to resolve the excessive theoretical prediction of the abundance of primordial lithium 7. We focus on the stau as a next-lightest superparticle, which is long lived due to its small mass difference with the lightest superparticle. It provides a number of additional decay processes of Li-7 and Be-7. A particularly important process is the internal conversion in the stau-nucleus bound state, which destroys the Li-7 and Be-7 effectively. We show that the modification can lead to a prediction consistent with the observed abundance of Li-7.