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.