Two nonstandard scenarios for pregalactic synthesis of the light elements (²H, ³He, ⁴He, and ⁷Li) are developed. Big bang photosynthesis occurs if energetic photons, produced by the decay of massive neutrinos or gravitinos, partially photodisintegrate ⁴He (formed in the standard hot big bang) to produce ²H and ³He. In this case, primordial nucleosynthesis no longer constrains the baryon density of the universe, or the number of neutrino species. Alternatively, one may dispense partially or completely with the hot big bang and produce the light elements by bombardment of primordial gas, provided that ⁴He is synthesized by a later generation of massive stars.
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Audouze et al. (1985) studied this question.