Lithium-6: A Probe of the Early Universe
Abstract
It is well known that useful constraints on the abundance of relic particles decaying after the epoch of Big Bang Nucleosynthesis may be derived from a possible overproduction of 3He and 2H. These nuclides result from the photodisintegration of 4He by gamma-rays from an electromagnetic cascade initiated by the decay of the out-of-equilibrium relic particles. I show that the products of the photodisintegration process (i.e. 3H, 3He) are energetic enough to synthesize 6Li via non-thermal nuclear reactions on 4He. The synthesized 6Li/H ratio may be compared to 6Li/H in metal-poor halo stars which, in the absence of stellar depletion of 6Li, yields already with current observational data more than an order of magnitude stronger constraints on relic particle densities than considerations of overproduction of 3He and 2H. In the advent that a plateau in 6Li/H ratios in metal-poor stars should be ever established, invaluable insight about the very early universe could be gained.Keywords
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