Did Something Decay, Evaporate, or Annihilate during Big Bang Nucleosynthesis?

Abstract

Results of a detailed examination of the cascade nucleosynthesis resulting from the putative hadronic decay, evaporation, or annihilation of a primordial relic during the Big Bang nucleosynthesis (BBN) era are presented. It is found that injection of energetic nucleons around cosmic time 1000 sec may lead to an observationally favored reduction of the primordial Li7/H yield by a factor 2 - 3. Moreover, such sources also generically predict the production of the Li6 isotope with magnitude close to the as yet unexplained high Li6 abundances in low-metallicity stars. The simplest of these models operate at fractional contribution to the baryon density Omega_b h^2> 0.025, slightly larger than that inferred from standard BBN. Though further study is required, such sources, as for example due to the decay of the next-to-lightest supersymmetric particle into GeV gravitinos or the decay of an unstable gravitino in the TeV range of abundance \Omega_G h^2\sim 5\times 10^{-4} show promise to explain both the Li6 and Li7 abundances in low metallicity stars.