Helium photodisintegration and nucleosynthesis: Implications for topological defects, high energy cosmic rays, and massive black holes

We consider the production of ³He and ²H by ⁴He photodisintegration initiated by nonthermal energy releases during early cosmic epochs. We find that this process cannot be the predominant source of primordial ²H since it would result in anomalously high ³He/D ratios in conflict with standard chemical evolution assumptions. We apply this fact to constrain topological defect models of highest energy cosmic ray (HECR) production. Such models have been proposed as possible sources of ultrahigh energy particles and {γ} rays with energies above 10²⁰ eV. The constraints on these models derived from ⁴He photodisintegration are compared to corresponding limits from spectral distortions of the cosmic microwave background radiation and from the observed diffuse {γ}-ray background. It is shown that for reasonable primary particle injection spectra superconducting cosmic strings, unlike ordinary strings or annihilating monopoles, cannot produce the HECR flux at the present epoch without violating at least the ⁴photodisintegration bound. The constraint from the diffuse {γ}-ray background rules out the dominant production of HECR by the decay of grand unification particles in models with cosmological evolution assuming standard fragmentation functions. Constraints on massive black hole induced photodisintegration are also discussed. {} 1995 The American Physical Society.