Lithium-6: A Probe of the Early Universe

I consider the synthesis of ⁶Li due to the decay of relic particles, such as gravitinos or moduli, after the epoch of big bang nucleosynthesis. The synthesized ⁶Li/H ratio may be compared to ⁶Li/H in metal-poor stars which, in the absence of stellar depletion of ⁶Li, yields significantly stronger constraints on relic particle densities than the usual consideration of overproduction of ³He. Production of ⁶Li during such an era of nonthermal nucleosynthesis may also be regarded as a possible explanation for the relatively high ⁶Li/H ratios observed in metal-poor halo stars.