Big bang photosynthesis and pregalactic nucleosynthesis of light elements

Abstract

Two nonstandard scenarios for pregalactic synthesis of the light elements (<SUP>2</SUP>H, <SUP>3</SUP>He, <SUP>4</SUP>He, and <SUP>7</SUP>Li) are developed. Big bang photosynthesis occurs if energetic photons, produced by the decay of massive neutrinos or gravitinos, partially photodisintegrate <SUP>4</SUP>He (formed in the standard hot big bang) to produce <SUP>2</SUP>H and <SUP>3</SUP>He. 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 <SUP>4</SUP>He is synthesized by a later generation of massive stars.